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* Copyright 1988-2007 University of Washington
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
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* ========================================================================
*/
IMAP Toolkit Frequently Asked Questions
Table of Contents
* 1. General/Software Feature Questions
+ 1.1 Can I set up a POP or IMAP server on UNIX/Linux/OSF/etc.?
+ 1.2 I am currently using qpopper as my POP3 server on UNIX.
Do I need to replace it with ipop3d in order to run imapd?
+ 1.3 Can I set up a POP or IMAP server on Windows XP, 2000,
NT, Me, 98, or 95?
+ 1.4 Can I set up a POP or IMAP server on Windows 3.1 or DOS?
+ 1.5 Can I set up a POP or IMAP server on Macintosh?
+ 1.6 Can I set up a POP or IMAP server on VAX/VMS?
+ 1.7 Can I set up a POP or IMAP server on TOPS-20?
+ 1.8 Are hierarchical mailboxes supported?
+ 1.9 Are "dual-use" mailboxes supported?
+ 1.10 Can I have a mailbox that has both messages and
sub-mailboxes?
+ 1.11 What is the difference between "mailbox" and "folder"?
+ 1.12 What is the status of internationalization?
+ 1.13 Can I use SSL?
+ 1.14 Can I use TLS and the STARTTLS facility?
+ 1.15 Can I use CRAM-MD5 authentication?
+ 1.16 Can I use APOP authentication?
+ 1.17 Can I use Kerberos V5?
+ 1.18 Can I use PAM for plaintext passwords?
+ 1.19 Can I use Kerberos 5 for plaintext passwords?
+ 1.20 Can I use AFS for plaintext passwords?
+ 1.21 Can I use DCE for plaintext passwords?
+ 1.22 Can I use the CRAM-MD5 database for plaintext passwords?
+ 1.23 Can I disable plaintext passwords?
+ 1.24 Can I disable plaintext passwords on unencrypted
sessions, but allow them on encrypted sessions?
+ 1.25 Can I use virtual hosts?
+ 1.26 Can I use RPOP authentication?
+ 1.27 Can I use Kerberos V4?
+ 1.28 Is there support for S/Key or OTP?
+ 1.29 Is there support for NTLM or SPA?
+ 1.30 Is there support for mh?
+ 1.31 Is there support for qmail and the maildir format?
+ 1.32 Is there support for the Cyrus mailbox format?
+ 1.33 Is this software Y2K compliant?
* 2. What Do I Need to Build This Software?
+ 2.1 What do I need to build this software with SSL on UNIX?
+ 2.2 What do I need to build this software with Kerberos V on
UNIX?
+ 2.3 What do I need to use a C++ compiler with this software
to build my own application?
+ 2.4 What do I need to build this software on Windows?
+ 2.5 What do I need to build this software on DOS?
+ 2.6 Can't I use Borland C to build this software on the PC?
+ 2.7 What do I need to build this software on the Mac?
+ 2.8 What do I need to build this software on VMS?
+ 2.9 What do I need to build this software on TOPS-20?
+ 2.10 What do I need to build this software on Amiga or OS/2?
+ 2.11 What do I need to build this software on Windows CE?
* 3. Build and Configuration Questions
+ 3.1 How do I configure the IMAP and POP servers on UNIX?
+ 3.2 I built and installed the servers according to the BUILD
instructions. It can't be that easy. Don't I need to write a
config file?
+ 3.3 How do I make the IMAP and POP servers look for INBOX at
some place other than the mail spool directory?
+ 3.4 How do I make the IMAP server look for secondary folders
at some place other than the user's home directory?
+ 3.5 How do I configure SSL?
+ 3.6 How do I configure TLS and the STARTTLS facility?
+ 3.7 How do I build/install OpenSSL and obtain/create
certificates for use with SSL?
+ 3.8 How do I configure CRAM-MD5 authentication?
+ 3.9 How do I configure APOP authentication?
+ 3.10 How do I configure Kerberos V5?
+ 3.11 How do I configure PAM for plaintext passwords?
+ 3.12 It looks like all I have to do to make the server use
Kerberos is to build with PAM on my Linux system, and set it
up in PAM for Kerberos passwords. Right?
+ 3.13 How do I configure Kerberos 5 for plaintext passwords?
+ 3.14 How do I configure AFS for plaintext passwords?
+ 3.15 How do I configure DCE for plaintext passwords?
+ 3.16 How do I configure the CRAM-MD5 database for plaintext
passwords?
+ 3.17 How do I disable plaintext passwords?
+ 3.18 How do I disable plaintext passwords on unencrypted
sessions, but allow them in SSL or TLS sessions?
+ 3.19 How do I configure virtual hosts?
+ 3.20 Why do I get compiler warning messages such as:
o passing arg 3 of `scandir' from incompatible pointer
type
o Pointers are not assignment-compatible.
o Argument #4 is not the correct type.
during the build?
+ 3.21 Why do I get compiler warning messages such as
o Operation between types "void(*)(int)" and "void*" is
not allowed.
o Function argument assignment between types "void*" and
"void(*)(int)" is not allowed.
o Pointers are not assignment-compatible.
o Argument #5 is not the correct type.
during the build?
+ 3.22 Why do I get linker warning messages such as:
o mtest.c:515: the `gets' function is dangerous and should
not be used.
during the build? Isn't this a security bug?
+ 3.23 Why do I get linker warning messages such as:
o auth_ssl.c:92: the `tmpnam' function is dangerous and
should not be used.
during the build? Isn't this a security bug?
+ 3.24 OK, suppose I see a warning message about a function
being "dangerous and should not be used" for something other
than this gets() or tmpnam() call?
* 4. Operational Questions
+ 4.1 How can I enable anonymous IMAP logins?
+ 4.2 How do I set up an alert message that each IMAP user will
see?
+ 4.3 How does the c-client library choose which of its several
mechanisms to use to establish an IMAP connection to the
server? I noticed that it can connect on port 143, port 993,
via rsh, and via ssh.
+ 4.4 I am using a TLS-capable IMAP server, so I don't need to
use /ssl to get encryption. However, I want to be certain
that my session is TLS encrypted before I send my password.
How to I do this?
+ 4.5 How do I use one of the alternative formats described in
the formats.txt document? In particular, I hear that mbx
format will give me better performance and allow shared
access.
+ 4.6 How do I set up shared mailboxes?
+ 4.7 How can I make the server syslogs go to someplace other
than the mail syslog?
* 5. Security Questions
+ 5.1 I see that the IMAP server allows access to arbitary
files on the system, including /etc/passwd! How do I disable
this?
+ 5.2 I've heard that IMAP servers are insecure. Is this true?
+ 5.3 How do I know that I have the most secure version of the
server?
+ 5.4 I see all these strcpy() and sprintf() calls, those are
unsafe, aren't they?
+ 5.5 Those /tmp lock files are protected 666, is that really
right?
* 6. Why Did You Do This Strange Thing? Questions
+ 6.1 Why don't you use GNU autoconfig / automake /
autoblurdybloop?
+ 6.2 Why do you insist upon a build with -g? Doesn't it waste
disk and memory space?
+ 6.3 Why don't you make c-client a shared library?
+ 6.4 Why don't you use iconv() for internationalization
support?
+ 6.5 Why is the IMAP server connected to the home directory by
default?
+ 6.6 I have a Windows system. Why isn't the server plug and
play for me?
+ 6.7 I looked at the UNIX SSL code and saw that you have the
SSL data payload size set to 8192 bytes. SSL allows 16K; why
aren't you using the full size?
+ 6.8 Why is an mh format INBOX called #mhinbox instead of just
INBOX?
+ 6.9 Why don't you support the maildir format?
+ 6.10 Why don't you support the Cyrus format?
+ 6.11 Why is it creating extra forks on my SVR4 system?
+ 6.12 Why are you so fussy about the date/time format in the
internal "From " line in traditional UNIX mailbox files? My
other mail program just considers every line that starts with
"From " to be the start of the message.
+ 6.13 Why is traditional UNIX format the default format?
+ 6.14 Why do you write this "DON'T DELETE THIS MESSAGE --
FOLDER INTERNAL DATA" message at the start of traditional
UNIX and MMDF format mailboxes?
+ 6.15 Why don't you stash the mailbox metadata in the first
real message of the mailbox instead of writing this fake
FOLDER INTERNAL DATA message?
+ 6.16 Why aren't "dual-use" mailboxes the default?
+ 6.17 Why do you use ucbcc to build on Solaris?
+ 6.18 Why should I care about some old system with BSD
libraries? cc is the right thing on my Solaris system!
+ 6.19 Why do you insist upon writing .lock files in the spool
directory?
+ 6.20 Why should I care about compatibility with the past?
* 7. Problems and Annoyances
+ 7.1 Help! My INBOX is empty! What happened to my messages?
+ 7.2 Help! All my messages in a non-INBOX mailbox have been
concatenated into one message which claims to be from me and
has a subject of the file name of the mailbox! What's going
on?
+ 7.3 Why do I get the message:
o CREATE failed: Can't create mailbox node xxxxxxxxx: File
exists
and how do I fix it?
+ 7.4 Why can't I log in to the server? The user name and
password are right!
+ 7.5 Help! My load average is soaring and I see hundreds of
POP and IMAP servers, many logged in as the same user!
+ 7.6 Why does mail disappear even though I set "keep mail on
server"?
+ 7.7 Why do I get the message
o Moved ##### bytes of new mail to /home/user/mbox from
/var/spool/mail/user
and why did this happen?
+ 7.8 Why isn't it showing the local host name as a
fully-qualified domain name?
+ 7.9 Why is the local host name in the From/Sender/Message-ID
headers of outgoing mail not coming out as a fully-qualified
domain name?
+ 7.10 What does the message:
o Mailbox vulnerable - directory /var/spool/mail must have
1777 protection
mean? How can I fix this?
+ 7.11 What does the message:
o Mailbox is open by another process, access is readonly
mean? How do I fix this?
+ 7.12 What does the message:
o Can't get write access to mailbox, access is readonly
mean?
+ 7.13 I set my POP3 client to "delete messages from server"
but they never get deleted. What is wrong?
+ 7.14 What do messages such as:
o Message ... UID ... already has UID ...
o Message ... UID ... less than ...
o Message ... UID ... greater than last ...
o Invalid UID ... in message ..., rebuilding UIDs
mean?
+ 7.15 What do the error messages:
o Unable to read internal header at ...
o Unable to find CRLF at ...
o Unable to parse internal header at ...
o Unable to parse message date at ...
o Unable to parse message flags at ...
o Unable to parse message UID at ...
o Unable to parse message size at ...
o Last message (at ... ) runs past end of file ...
mean? I am using mbx format.
+ 7.16 What do the syslog messages:
o imap/tcp server failing (looping)
o pop3/tcp server failing (looping)
mean? When it happens, the listed service shuts down. How can
I fix this?
+ 7.17 What does the syslog message:
o Mailbox lock file /tmp/.600.1df3 open failure:
Permission denied
mean?
+ 7.18 What do the syslog messages:
o Command stream end of file, while reading line user=...
host=...
o Command stream end of file, while reading char user=...
host=...
o Command stream end of file, while writing text user=...
host=...
mean?
+ 7.19 Why did my POP or IMAP session suddenly disconnect? The
syslog has the message:
o Killed (lost mailbox lock) user=... host=...
+ 7.20 Why does my IMAP client show all the files on the
system, recursively from the UNIX root directory?
+ 7.21 Why does my IMAP client show all of my files,
recursively from my UNIX home directory?
+ 7.22 Why does my IMAP client show that I have mailboxes named
"#mhinbox", "#mh", "#shared", "#ftp", "#news", and "#public"?
+ 7.23 Why does my IMAP client show all my files in my home
directory?
+ 7.24 Why is there a long delay before I get connected to the
IMAP or POP server, no matter what client I use?
+ 7.25 Why is there a long delay in Pine or any other c-client
based application call before I get connected to the IMAP
server? The hang seems to be in the c-client mail_open()
call. I don't have this problem with any other IMAP client.
There is no delay connecting to a POP3 or NNTP server with
mail_open().
+ 7.26 Why does a message sometimes get split into two or more
messages on my SUN system?
+ 7.27 Why did my POP or IMAP session suddenly disconnect? The
syslog has the message:
o Autologout user=<...my user name...> host=<...my imap
server...>
+ 7.28 What does the UNIX error message:
o TLS/SSL failure: myserver: SSL negotiation failed
mean?
+ 7.29 What does the PC error message:
o TLS/SSL failure: myserver: Unexpected TCP input
disconnect
mean?
+ 7.30 What does the error message:
o TLS/SSL failure: myserver: Server name does not match
certificate
mean?
+ 7.31 What does the UNIX error message:
o TLS/SSL failure: myserver: self-signed certificate
mean?
+ 7.32 What does the PC error message
o TLS/SSL failure: myserver: Self-signed certificate or
untrusted authority
mean?
+ 7.33 What does the UNIX error message:
o TLS/SSL failure: myserver: unable to get local issuer
certificate
mean?
+ 7.34 Why does reading certain messages hang when using
Netscape? It works fine with Pine!
+ 7.35 Why does Netscape say that there's a problem with the
IMAP server and that I should "Contact your mail server
administrator."?
+ 7.36 Why is one user creating huge numbers of IMAP or POP
server sessions?
+ 7.37 Why don't I get any new mail notifications from Outlook
Express or Outlook after a while?
+ 7.38 Why don't I get any new mail notifications from
Entourage?
+ 7.39 Why doesn't Entourage work at all?
+ 7.40 Why doesn't Netscape Notify (NSNOTIFY.EXE) work at all?
+ 7.41 Why can't I connect via SSL to Eudora? It says the
connection has been broken, and in the server syslogs I see
"Command stream end of file".
+ 7.42 Sheesh. Aren't there any good IMAP clients out there?
+ 7.43 But wait! PC Pine (or other PC program build with
c-client) crashes with the message
o incomplete SecBuffer exceeds maximum buffer size
when I use SSL connections. This is a bug in c-client, right?
+ 7.44 My qpopper users keep on getting the DON'T DELETE THIS
MESSAGE -- FOLDER INTERNAL DATA if they also use Pine or
IMAP. How can I fix this?
+ 7.45 Help! I installed the servers but I can't connect to
them from my client!
+ 7.46 Why do I get the message
o Can not authenticate to SMTP server: 421 SMTP connection
went away!
and why did this happen? There was also something about
o SECURITY PROBLEM: insecure server advertised AUTH=PLAIN
+ 7.47 Why do I get the message
o SMTP Authentication cancelled
and why did this happen? There was also something about
o SECURITY PROBLEM: insecure server advertised AUTH=PLAIN
+ 7.48 Why do I get the message
o Invalid base64 string
when I try to authenticate to a Cyrus server?
* 8. Where to Go For Additional Information
+ 8.1 Where can I go to ask questions?
+ 8.2 I have some ideas for enhancements to IMAP. Where should
I go?
+ 8.3 Where can I read more about IMAP and other email
protocols?
+ 8.4 Where can I find out more about setting up and
administering an IMAP server?
_________________________________________________________________
1. General/Software Feature Questions
_________________________________________________________________
1.1 Can I set up a POP or IMAP server on UNIX/Linux/OSF/etc.?
Yes. Refer to the UNIX specific notes in files CONFIG and
BUILD.
_________________________________________________________________
1.2 I am currently using qpopper as my POP3 server on UNIX. Do I need
to replace it with ipop3d in order to run imapd?
Not necessarily.
Although ipop3d interoperates with imapd better than qpopper,
imapd and qpopper will work together. The few qpopper/imapd
interoperability issues mostly affect users who use both IMAP
and POP3 clients; those users would probably be better served
if their POP3 server is ipop3d.
If you are happy with qpopper and just want to add imapd, you
should do that, and defer a decision on changing qpopper to
ipop3d. That way, you can get comfortable with imapd's
performance, without changing anything for your qpopper users.
Many sites have subsequently decided to change from qpopper to
ipop3d in order to get better POP3/IMAP interoperability. If
you need to do this, you'll know. There also seems to be a way
to make qpopper work better with imapd; see the answer to the
My qpopper users keep on getting the DON'T DELETE THIS MESSAGE
-- FOLDER INTERNAL DATA if they also use Pine or IMAP. How can
I fix this? question.
_________________________________________________________________
1.3 Can I set up a POP or IMAP server on Windows XP, 2000, NT, Me, 98,
or 95?
Yes. Refer to the NT specific notes in files CONFIG and BUILD.
Also, for DOS-based versions of Windows (Windows Me, 98, and
95) you *must* set up CRAM-MD5 authentication, as described in
md5.txt.
There is no file access control on Windows 9x or Me, so you
probably will have to do modifications to env_unix.c to prevent
people from hacking others' mail.
Note, however, that the server is not plug and play the way it
is for UNIX.
_________________________________________________________________
1.4 Can I set up a POP or IMAP server on Windows 3.1 or DOS?
1.5 Can I set up a POP or IMAP server on Macintosh?
1.6 Can I set up a POP or IMAP server on VAX/VMS?
Yes, it's just a small matter of programming.
_________________________________________________________________
1.7 Can I set up a POP or IMAP server on TOPS-20?
You have a TOPS-20 system? Cool.
If IMAP2 (RFC 1176) is good enough for you, you can use MAPSER
which is about the ultimate gonzo pure TOPS-20 extended
addressing assembly language program. Unfortunately, IMAP2 is
barely good enough for Pine these days, and most other IMAP
clients won't work with IMAP2 at all. Maybe someone will hack
MAPSER to do IMAP4rev1 some day.
We don't know if anyone wrote a POP3 server for TOPS-20. There
definitely was a POP2 server once upon a time.
Or you can port the POP and IMAP server from this IMAP toolkit
to it. All that you need for a first stab is to port the MTX
driver. That'll probably be just a couple of hours of hacking.
_________________________________________________________________
1.8 Are hierarchical mailboxes supported?
1.9 Are "dual-use" mailboxes supported?
1.10 Can I have a mailbox that has both messages and sub-mailboxes?
Yes. However, there is one important caveat.
Some mailbox formats, including the default which is the
traditional UNIX mailbox format, are stored as a single file
containing all the messages. UNIX does not permit a name in the
filesystem to be both a file and a directory; consequently you
can not have a sub-mailbox within a mailbox that is in one of
these formats.
This is not a limitation of the software; this is a limitation
of UNIX. For example, there are mailbox formats in which the
name is a directory and each message is a file within that
directory; these formats support sub-mailboxes within such
mailboxes. However, for technical reasons, the "flat file"
formats are generally preferred since they perform better. Read
imap-2007/docs/formats.txt for more information on this topic.
It is always permissible to create a directory that is not a
mailbox, and have sub-mailboxes under it. The easiest way to
create a directory is to create a new mailbox inside a
directory that doesn't already exist. For example, if you
create "Mail/testbox" on UNIX, the directory "Mail/" will
automatically be created and then the mailbox "testbox" will be
created as a sub-mailbox of "Mail/".
It is also possible to create the name "Mail/" directly. Check
the documentation for your client software to see how to do
this with that software.
Of course, on Windows systems you would use "\" instead of "/".
_________________________________________________________________
1.11 What is the difference between "mailbox" and "folder"?
The term "mailbox" is IMAP-speak for what a lot of software
calls a "folder" or a "mail folder". However, "folder" is often
used in other contexts to refer to a directory, for example, in
the graphic user interface on both Windows and Macintosh.
A "mailbox" is specifically defined as a named object that
contains messages. It is not required to be capable of
containing other types of objects including other mailboxes;
although some mailbox formats will permit this.
In IMAP-speak, a mailbox which can not contain other mailboxes
is called a "no-inferiors mailbox". Similarly, a directory
which can not contain messages is not a mailbox and is called a
"no-select name".
_________________________________________________________________
1.12 What is the status of internationalization?
The IMAP toolkit is partially internationalized and
multilingualized.
Searching is supported in the following charsets: US-ASCII,
UTF-8, ISO-8859-1, ISO-8859-2, ISO-8859-3, ISO-8859-4,
ISO-8859-5, ISO-8859-6, ISO-8859-7, ISO-8859-8, ISO-8859-9,
ISO-8859-10, ISO-8859-11, ISO-8859-13, ISO-8859-14,
ISO-8859-15, ISO-8859-16, KOI8-R, KOI8-U (alias KOI8-RU),
TIS-620, VISCII, ISO-2022-JP, ISO-2022-KR, ISO-2022-CN,
ISO-2022-JP-1, ISO-2022-JP-2, GB2312 (alias CN-GB),
CN-GB-12345, BIG5 (alias CN-BIG5), EUC-JP, EUC-KR, Shift_JIS,
Shift-JIS, KS_C_5601-1987, KS_C_5601-1992, WINDOWS_874,
WINDOWS-1250, WINDOWS-1251, WINDOWS-1252, WINDOWS-1253,
WINDOWS-1254, WINDOWS-1255, WINDOWS-1256, WINDOWS-1257,
WINDOWS-1258.
All ISO-2022-?? charsets are treated identically, and support
ASCII, JIS Roman, hankaku katakana, ISO-8859-[1 - 10], TIS, GB
2312, JIS X 0208, JIS X 0212, KSC 5601, and planes 1 and 2 of
CNS 11643.
EUC-JP includes support for JIS X 0212 and hankaku katakana.
c-client library support also exists to convert text in any of
the above charsets into Unicode, including headers with MIME
encoded-words.
There is no support for localization (e.g. non-English error
messages) at the present time, but such support is planned.
_________________________________________________________________
1.13 Can I use SSL?
Yes. See the answer to the How do I configure SSL? question.
_________________________________________________________________
1.14 Can I use TLS and the STARTTLS facility?
Yes. See the answer to the How do I configure TLS and the
STARTTLS facility? question.
_________________________________________________________________
1.15 Can I use CRAM-MD5 authentication?
Yes. See the answer to the How do I configure CRAM-MD5
authentication? question.
_________________________________________________________________
1.16 Can I use APOP authentication?
Yes. See the How do I configure APOP authentication? question.
Note that there is no client support for APOP authentication.
_________________________________________________________________
1.17 Can I use Kerberos V5?
Yes. See the answer to the How do I configure Kerberos V5?
question.
_________________________________________________________________
1.18 Can I use PAM for plaintext passwords?
Yes. See the answer to the How do I configure PAM for plaintext
passwords? question.
_________________________________________________________________
1.19 Can I use Kerberos 5 for plaintext passwords?
Yes. See the answer to the How do I configure Kerberos 5 for
plaintext passwords? question.
_________________________________________________________________
1.20 Can I use AFS for plaintext passwords?
Yes. See the answer to the How do I configure AFS for plaintext
passwords? question.
_________________________________________________________________
1.21 Can I use DCE for plaintext passwords?
Yes. See the answer to the How do I configure DCE for plaintext
passwords? question.
_________________________________________________________________
1.22 Can I use the CRAM-MD5 database for plaintext passwords?
Yes. See the answer to the How do I configure the CRAM-MD5
database for plaintext passwords? question.
_________________________________________________________________
1.23 Can I disable plaintext passwords?
Yes. See the answer to the How do I disable plaintext
passwords? question.
_________________________________________________________________
1.24 Can I disable plaintext passwords on unencrypted sessions, but
allow them on encrypted sessions?
Yes. See the answer to the How do I disable plaintext passwords
on unencrypted sessions, but allow them in SSL or TLS sessions?
question.
_________________________________________________________________
1.25 Can I use virtual hosts?
Yes. See the answer to the How do I configure virtual hosts?
question.
_________________________________________________________________
1.26 Can I use RPOP authentication?
There is no support for RPOP authentication.
_________________________________________________________________
1.27 Can I use Kerberos V4?
Kerberos V4 is not supported. Kerberos V4 client-only
contributed code is available in
ftp://ftp.cac.washington.edu/mail/kerberos4-patches.tar.Z
This is a patchkit which must be applied to the IMAP toolkit
according to the instructions in the patchkit's README. We can
not promise that this code works.
_________________________________________________________________
1.28 Is there support for S/Key or OTP?
There is currently no support for S/Key or OTP. There may be an
OTP SASL authenticator available from third parties.
_________________________________________________________________
1.29 Is there support for NTLM or SPA?
There is currently no support for NTLM or SPA, nor are there
any plans to add such support. In general, I avoid
vendor-specific mechanisms. I also believe that these
mechanisms are being deprecated by their vendor.
There may be an NTLM SASL authenticator available from third
parties.
_________________________________________________________________
1.30 Is there support for mh?
Yes, but only as a legacy format. Your mh format INBOX is
accessed by the name "#mhinbox", and all other mh format
mailboxes are accessed by prefixing "#mh/" to the name, e.g.
"#mh/foo". The mh support uses the "Path:" entry in your
.mh_profile file to identify the root directory of your mh
format mailboxes.
Non-legacy use of mh format is not encouraged. There is no
support for permanent flags or unique identifiers; furthermore
there are known severe performance problems with the mh format.
_________________________________________________________________
1.31 Is there support for qmail and the maildir format?
There is no support for qmail or the maildir format in our
distribution, nor are there any plans to add such support.
Maildir support may be available from third parties.
_________________________________________________________________
1.32 Is there support for the Cyrus mailbox format?
No.
_________________________________________________________________
1.33 Is this software Y2K compliant?
Please read the files Y2K and calendar.txt.
_________________________________________________________________
2. What Do I Need to Build This Software?
_________________________________________________________________
2.1 What do I need to build this software with SSL on UNIX?
You need to build and install OpenSSL first.
_________________________________________________________________
2.2 What do I need to build this software with Kerberos V on UNIX?
You need to build and install MIT Kerberos first.
_________________________________________________________________
2.3 What do I need to use a C++ compiler with this software to build
my own application?
If you are building an application using the c-client library,
use the new c-client.h file instead of including the other
include files. It seems that c-client.h should define away all
the troublesome names that conflict with C++.
If you use gcc, you may need to use -fno-operator-names as
well.
_________________________________________________________________
2.4 What do I need to build this software on Windows?
You need Microsoft Visual C++ 6.0, Visual C++ .NET, or Visual
C# .NET (which you can buy from any computer store), along with
the Microsoft Platform SDK (which you can download from
Microsoft's web site).
You do not need to install the entire Platform SDK; it suffices
to install just the Core SDK and the Internet Development SDK.
_________________________________________________________________
2.5 What do I need to build this software on DOS?
It's been several years since we last attempted to do this. At
the time, we used Microsoft C.
_________________________________________________________________
2.6 Can't I use Borland C to build this software on the PC?
Probably not. If you know otherwise, please let us know.
_________________________________________________________________
2.7 What do I need to build this software on the Mac?
It has been several years since we last attempted to do this.
At the time, we used Symantec THINK C; but today you'll need a
C compiler which allows segments to be more than 32K.
_________________________________________________________________
2.8 What do I need to build this software on VMS?
You need the VMS C compiler, and either the Multinet or Netlib
TCP.
_________________________________________________________________
2.9 What do I need to build this software on TOPS-20?
You need the TOPS-20 KCC compiler.
_________________________________________________________________
2.10 What do I need to build this software on Amiga or OS/2?
We don't know.
_________________________________________________________________
2.11 What do I need to build this software on Windows CE?
This port is incomplete. Someone needs to finish it.
_________________________________________________________________
3. Build and Configuration Questions
_________________________________________________________________
3.1 How do I configure the IMAP and POP servers on UNIX?
3.2 I built and installed the servers according to the BUILD
instructions. It can't be that easy. Don't I need to write a config
file?
For ordinary "vanilla" UNIX systems, this software is plug and
play; just build it, install it, and you're done. If you have a
modified system, then you may want to do additional work; most
of this is to a single source code file (env_unix.c on UNIX
systems). Read the file CONFIG for more details.
Yes, it's that easy. There are some additional options, such as
SSL or Kerberos, which require additional steps to build. See
the relevant questions below.
_________________________________________________________________
3.3 How do I make the IMAP and POP servers look for INBOX at some
place other than the mail spool directory?
3.4 How do I make the IMAP server look for secondary folders at some
place other than the user's home directory?
Please read the file CONFIG for discussion of this and other
issues.
_________________________________________________________________
3.5 How do I configure SSL?
3.6 How do I configure TLS and the STARTTLS facility?
imap-2007 supports SSL and TLS client functionality on UNIX and
32-bit Windows for IMAP, POP3, SMTP, and NNTP; and SSL and TLS
server functionality on UNIX for IMAP and POP3.
UNIX SSL build requires that a third-party software package,
OpenSSL, be installed on the system first. Read
imap-2007/docs/SSLBUILD for more information.
SSL is supported via undocumented Microsoft interfaces in
Windows 9x and NT4; and via standard interfaces in Windows
2000, Windows Millenium, and Windows XP.
_________________________________________________________________
3.7 How do I build/install OpenSSL and obtain/create certificates for
use with SSL?
If you need help in doing this, try the contacts mentioned in
the OpenSSL README. We do not offer support for OpenSSL or
certificates.
_________________________________________________________________
3.8 How do I configure CRAM-MD5 authentication?
3.9 How do I configure APOP authentication?
CRAM-MD5 authentication is enabled in the IMAP and POP3 client
code on all platforms. Read md5.txt to learn how to set up
CRAM-MD5 and APOP authentication on UNIX and NT servers.
There is no support for APOP client authentication.
_________________________________________________________________
3.10 How do I configure Kerberos V5?
imap-2007 supports client and server functionality on UNIX and
32-bit Windows.
Kerberos V5 is supported by default in Windows 2000 builds:
nmake -f makefile.w2k
Other builds require that a third-party Kerberos package, e.g.
MIT Kerberos, be installed on the system first.
To build with Kerberos V5 on UNIX, include
EXTRAAUTHENTICATORS=gss in the make command line, e.g.
make lnp EXTRAAUTHENTICATORS=gss
To build with Kerberos V5 on Windows 9x, Windows Millenium, and
NT4, use the "makefile.ntk" file instead of "makefile.nt":
nmake -f makefile.ntk
_________________________________________________________________
3.11 How do I configure PAM for plaintext passwords?
On Linux systems, use the lnp port, e.g.
make lnp
On Solaris systems and other systems with defective PAM
implementations, build with PASSWDTYPE=pmb, e.g.
make sol PASSWDTYPE=pmb
On all other systems, build with PASSWDTYPE=pam, e.g
make foo PASSWDTYPE=pam
If you build with PASSWDTYPE=pam and authentication does not
work, try rebuilding (after a "make clean") with
PASSWDTYPE=pmb.
_________________________________________________________________
3.12 It looks like all I have to do to make the server use Kerberos is
to build with PAM on my Linux system, and set it up in PAM for
Kerberos passwords. Right?
Yes and no.
Doing this will make plaintext password authentication use the
Kerberos password instead of the /etc/passwd password.
However, this will NOT give you Kerberos-secure authentication.
See the answer to the How do I configure Kerberos V5? question
for how to build with Kerberos-secure authentication.
_________________________________________________________________
3.13 How do I configure Kerberos 5 for plaintext passwords?
Build with PASSWDTYPE=gss, e.g.
make sol PASSWDTYPE=gss
However, this will NOT give you Kerberos-secure authentication.
See the answer to the How do I configure Kerberos V5? question
for how to build with Kerberos-secure authentication.
_________________________________________________________________
3.14 How do I configure AFS for plaintext passwords?
Build with PASSWDTYPE=afs, e.g
make sol PASSWDTYPE=afs
_________________________________________________________________
3.15 How do I configure DCE for plaintext passwords?
Build with PASSWDTYPE=dce, e.g
make sol PASSWDTYPE=dce
_________________________________________________________________
3.16 How do I configure the CRAM-MD5 database for plaintext passwords?
The CRAM-MD5 password database is automatically used for
plaintext password if it exists.
Note that this is NOT CRAM-MD5-secure authentication. You
probably want to consider disabling plaintext passwords for
non-SSL/TLS sessions. See the next two questions.
_________________________________________________________________
3.17 How do I disable plaintext passwords?
Server-level plaintext passwords can be disabled by setting
PASSWDTYPE=nul, e.g.
make lnx EXTRAAUTHENTICATORS=gss PASSWDTYPE=nul
Note that you must have a CRAM-MD5 database installed or
specify at least one EXTRAAUTHENTICATOR, otherwise it will not
be possible to log in to the server.
When plaintext passwords are disabled, the IMAP server will
advertise the LOGINDISABLED capability and the POP3 server will
not advertise the USER capability.
3.18 How do I disable plaintext passwords on unencrypted sessions, but
allow them in SSL or TLS sessions?
Do not set PASSWDTYPE=nul or SSLTYPE=unix. Set SSLTYPE=nopwd
instead, e.g.
make lnx SSLTYPE=nopwd
When plaintext passwords are disabled, the IMAP server will
advertise the LOGINDISABLED capability and the POP3 server will
not advertise the USER capability.
Plaintext passwords will always be enabled in SSL sessions; the
IMAP server will not advertise the LOGINDISABLED capability and
the POP3 server will advertise the USER capability.
If the client does a successful start-TLS in a non-SSL session,
plaintext passwords will be enabled, and a new CAPABILITY or
CAPA command (which is required after start-TLS) will show the
effect as in SSL sessions.
_________________________________________________________________
3.19 How do I configure virtual hosts?
This is automatic, but with certain restrictions.
The most important one is that each virtual host must have its
own IP address; otherwise the server has no way of knowing
which virtual host is desired.
As distributed, the software uses a global password file; hence
user "fred" on one virtual host is "fred" on all virtual hosts.
You may want to modify the checkpw() routine to implement some
other policy (e.g. separate password files).
Note that the security model assumes that all users have their
own unique UNIX UID number. So if you use separate password
files you should make certain that the UID numbers do not
overlap between different files.
More advanced virtual host support may be available as patches
from third parties.
_________________________________________________________________
3.20 Why do I get compiler warning messages such as:
passing arg 3 of `scandir' from incompatible pointer type
Pointers are not assignment-compatible.
Argument #4 is not the correct type.
during the build?
You can safely ignore these messages.
Over the years, the prototype for scandir() has changed, and
thus is variant across different UNIX platforms. In particular,
the definitions of the third argument (type select_t) and
fourth argument (type compar_t) have changed over the years,
the issue being whether or not the arguments to the functions
pointed to by these function pointers are of type const or not.
The way that c-client calls scandir() will tend to generate
these compiler warnings on newer systems such as Linux;
however, it will still build. The problem with fixing the call
is that then it won't build on older systems.
_________________________________________________________________
3.21 Why do I get compiler warning messages such as
Operation between types "void(*)(int)" and "void*" is not allowed.
Function argument assignment between types "void*" and "void(*)(int)" is not a
llowed.
Pointers are not assignment-compatible.
Argument #5 is not the correct type.
during the build?
You can safely ignore these messages.
All known systems have no problem with casting a function
pointer to/from a void* pointer, certain C compilers issue a
compiler diagnostic because this facility is listed as a
"Common extension" by the C standard:
K.5.7 Function pointer casts
[#1] A pointer to an object or to void may be cast to a pointer
to a function, allowing data to be invoked as a function (6.3.4).
[#2] A pointer to a function may be cast to a pointer to an
object or to void, allowing a function to be inspected or
modified (for example, by a debugger) (6.3.4).
It may be just a "common extension", but this facility is
relied upon heavily by c-client.
_________________________________________________________________
3.22 Why do I get linker warning messages such as:
mtest.c:515: the `gets' function is dangerous and should not be used.
during the build? Isn't this a security bug?
You can safely ignore this message.
Certain linkers, most notably on Linux, give this warning
message. It is indeed true that the traditional gets() function
is not a safe one.
However, the mtest program is only a demonstration program, a
model of a very basic application program using c-client. It is
not something that you would install, much less run in any
security-sensitive context.
mtest has numerous other shortcuts that you wouldn't want to do
in a real application program.
The only "security bug" with mtest would be if it was run by
some script in a security-sensitive context, but mtest isn't
particularly useful for such purposes. If you wanted to write a
script to automate some email task using c-client, you'd be
better off using imapd instead of mtest.
mtest only has two legitimate uses. It's a useful testbed for
me when debugging new versions of c-client, and it's useful as
a model for someone writing a simple c-client application to
see how the various calls work.
By the way, if you need a more advanced example of c-client
programming than mtest (and you probably will), I recommend
that you look at the source code for imapd and Pine.
_________________________________________________________________
3.23 Why do I get linker warning messages such as:
auth_ssl.c:92: the `tmpnam' function is dangerous and should not be used.
during the build? Isn't this a security bug?
You can safely ignore this message.
Certain linkers, most notably on Linux, give this warning
message, based upon two known issues with tmpnam():
there can be a buffer overflow if an inadequate buffer is
allocated.
there can be a timing race caused by certain incautious
usage of the return value.
Neither of these issues applies in the particular use that is
made of tmpnam(). More importantly, the tmpnam() call is never
executed on Linux systems.
_________________________________________________________________
3.24 OK, suppose I see a warning message about a function being
"dangerous and should not be used" for something other than this
gets() or tmpnam() call?
Please forward the details for investigation.
_________________________________________________________________
4. Operational Questions
_________________________________________________________________
4.1 How can I enable anonymous IMAP logins?
Create the file /etc/anonymous.newsgroups. At the present time,
this file should be empty. This will permit IMAP logins as
anonymous as well as the ANONYMOUS SASL authenticator.
Anonymous users have access to mailboxes in the #news., #ftp/,
and #public/ namespaces only.
_________________________________________________________________
4.2 How do I set up an alert message that each IMAP user will see?
Create the file /etc/imapd.alert with the text of the message.
This text should be kept to one line if possible. Note that
this will cause an alert to every IMAP user every time they
initiate an IMAP session, so it should only be used for
critical messages.
_________________________________________________________________
4.3 How does the c-client library choose which of its several
mechanisms to use to establish an IMAP connection to the server? I
noticed that it can connect on port 143, port 993, via rsh, and via
ssh.
c-client chooses how to establish an IMAP connection via the
following rules:
+ If /ssl is specified, use an SSL connection. Fail otherwise.
+ Else if client is a UNIX system and "ssh server exec
/etc/rimapd" works, use that
+ Else if /tryssl is specified and an SSL connection works, use
that.
+ Else if client is a UNIX system and "rsh server exec
/etc/rimapd" works, use that.
+ Else use a non-SSL connection.
_________________________________________________________________
4.4 I am using a TLS-capable IMAP server, so I don't need to use /ssl
to get encryption. However, I want to be certain that my session is
TLS encrypted before I send my password. How to I do this?
Use the /tls option in the mailbox name. This will cause an
error message and the connection to fail if the server does not
negotiate STARTTLS.
_________________________________________________________________
4.5 How do I use one of the alternative formats described in the
formats.txt document? In particular, I hear that mbx format will give
me better performance and allow shared access.
The rumors about mbx format being preferred are true. It is
faster than the traditional UNIX mailbox format and permits
shared access.
However, and this is very important, note that using an
alternative mailbox format is an advanced facility, and only
expert users should undertake it. If you don't understand any
of the following notes, you may not be enough of an expert yet,
and are probably better off not going this route until you are
more comfortable with your understanding.
Some of the formats, including mbx, are only supported by the
software based on the c-client library, and are not recognized
by other mailbox programs. The "vi" editor will corrupt any mbx
format mailbox that it encounters.
Another problem is that the certain formats, including mbx, use
advanced file access and locking techniques that do not work
reliably with NFS. NFS is not a real filesystem. Use IMAP
instead of NFS for distributed access.
Each of the following steps are in escalating order of
involvement. The further you go down this list, the more deeply
committed you become:
+ The simplest way to create a mbx-format mailbox is to prefix
the name with "#driver.mbx/" when creating a mailbox through
c-client. For example, if you create "#driver.mbx/foo", the
mailbox "foo" will be created in mbx format. Only use
"#driver.mbx/" when creating the mailbox. At all other times,
just use the name ("foo" in this example); the software will
automatically select the driver for mbx whenever that mailbox
is accessed without you doing anything else.
+ You can use the "mailutil copy" command to copy an existing
mailbox to a new mailbox in mbx format. Read the man page
provided with the mailutil program for details.
+ If you create an mbx-format INBOX, by creating
"#driver.mbx/INBOX" (note that "INBOX" must be all
uppercase), then subsequent access to INBOX by any c-client
based application will use the mbx-format INBOX. Any mail
delivered to the traditional format mailbox in the spool
directory (e.g. /var/spool/mail/$USER) will automatically be
copied into the mbx-format INBOX and the spool directory copy
removed.
+ You can cause any newly-created mailboxes to be in mbx-format
by default by changing the definition of
CREATEPROTO=unixproto to be CREATEPROTO=mbxproto in
src/osdep/unix/Makefile, then rebuilding the IMAP toolkit (do
a "make clean" first). Do not change EMPTYPROTO, since mbx
format mailboxes are never a zero-byte file. If you use Pine
or the imap-utils, you should probably also rebuild them with
the new IMAP toolkit too.
+ You can deliver directly to the mbx-format INBOX by use of
the tmail or dmail programs. tmail is for direct invocation
from sendmail (or whatever MTA program you use); dmail is for
calls from procmail. Both of these programs have man pages
which must be read carefully before making this change.
Most other servers (e.g. Cyrus) require use of a non-standard
format. A full-fledged format conversion is not significantly
different from what you have to do with other servers. The
difference, which makes format conversion procedures somewhat
more complicated with this server, is that there is no "all or
nothing" requirement with this server. There are many points in
between. A format conversion can be anything from a single
mailbox or single user, to systemwide.
This is good in that you can decide how far to go, or do the
steps incrementally as you become more comfortable with the
result. On the other hand, there's no "One True Way" which can
be boiled down to a simple set of pedagogical instructions.
A number of sites have done full-fledged format conversions,
and are reportedly quite happy with the results. Feel free to
ask in the comp.mail.imap newsgroup or the imap-uw mailing
list for advice or help.
_________________________________________________________________
4.6 How do I set up shared mailboxes?
At the simplest level, a shared mailbox is one which has UNIX
file and directory protections which permit multiple users to
access it. What this means is that your existing skills and
tools to create and manage shared files on your UNIX system
apply to shared mailboxes; e.g.
chmod 666 mailbox
You may want to consider the use of a mailbox format which
permits multiple simultaneous read/write sessions, such as the
mbx format. The traditional UNIX format only allows one
read/write session to a mailbox at a time.
An additional convenience item are three system directories,
which can be set up for shared namespaces. These are: #ftp,
#shared, and #public, and are defined by creating the
associated UNIX users and home directories as described below.
#ftp/ refers to the anonymous ftp filesystem exported by the
ftp server, and is equivalent to the home directory for UNIX
user "ftp". For example, #ftp/foo/bar refers to the file
/foo/bar in the anonymous FTP filesystem, or ~ftp/foo/bar for
normal users. Anonymous FTP files are available to anonymous
IMAP logins. By default, newly-created files in #ftp/ are
protected 644.
#public/ refers to an IMAP toolkit convention called "public"
files, and is equivalent to the home directory for UNIX user
"imappublic". For example, #public/foo/bar refers to the file
~imappublic/foo/bar. Public files are available to anonymous
IMAP logins. By default, newly-created files in #public are
created with protection 0666.
#shared/ refers to an IMAP toolkit convention called "shared"
files, and is equivalent to the home directory for UNIX user
"imapshared". For example, #shared/foo/bar refers to the file
~imapshared/foo/bar. Shared files are not available to
anonymous IMAP logins. By default, newly-created files in
#shared are created with protection 0660.
_________________________________________________________________
4.7 How can I make the server syslogs go to someplace other than the
mail syslog?
The openlog() call that sets the syslog facility is in
src/osdep/unix/env_unix.c in routine server_init(). You need to
edit this file to change the syslog facility from LOG_MAIL to
the facility you want, then rebuild. You also need to set up
your /etc/syslog.conf properly.
Refer to the man pages for syslog and syslogd for more
information on what the available syslog facilities are and how
to configure syslogs. If you still don't understand what to do,
find a UNIX system expert.
_________________________________________________________________
5. Security Questions
_________________________________________________________________
5.1 I see that the IMAP server allows access to arbitary files on the
system, including /etc/passwd! How do I disable this?
You should not worry about this if your IMAP users are allowed
shell access. The IMAP server does not permit any access that
the user can not have via the shell.
If, and only if, you deny your IMAP users shell access, you may
want to consider one of three choices. Note that these choices
reduce IMAP functionality, and may have undesirable side
effects. Each of these choices involves an edit to file
src/osdep/unix/env_unix.c
The first (and recommended) choice is to set restrictBox as
described in file CONFIG. This will disable access to the
filesystem root, to other users' home directory, and to
superior directory.
The second (and strongly NOT recommended) choice is to set
closedBox as described in file CONFIG. This puts each IMAP
session into a so-called "chroot jail", and thus setting this
option is extremely dangerous; it can make your system much
less secure and open to root compromise attacks. So do not use
this option unless you are absolutely certain that you
understand all the issues of a "chroot jail."
The third choice is to rewrite routine mailboxfile() to
implement whatever mapping from mailbox name to filesystem name
(and restrictions) that you wish. This is the most general
choice. As a guide, you can see at the start of routine
mailboxfile() what the restrictBox choice does.
_________________________________________________________________
5.2 I've heard that IMAP servers are insecure. Is this true?
There are no known security problems in this version of the
IMAP toolkit, including the IMAP and POP servers. The IMAP and
POP servers limit what can be done while not logged in, and as
part of the login process discard all privileges except those
of the user.
As with other software packages, there have been buffer
overflow vulnerabilities in past versions. All known problems
of this nature are fixed in this version.
There is every reason to believe that the bad guys are engaged
in an ongoing effort to find vulnerabilities in the IMAP
toolkit. We look for such problems, and when one is found we
fix it.
It's unfortunate that any vulnerabilities existed in past
versions, and we're doing my best to keep the IMAP toolkit free
of vulnerabilities. No new vulnerabilities have been discovered
in quite a while, but efforts will not be relaxed.
Beware of vendors who claim that their implementations can not
have vulnerabilities.
_________________________________________________________________
5.3 How do I know that I have the most secure version of the server?
The best way is to keep your server software up to date. The
bad guys are always looking for ways to crack software, and
when they find one, let all their friends know.
Oldtimers used to refer to a concept of software rot: if your
software hasn't been updated in a while, it would "rot" -- tend
to acquire problems that it didn't have when it was new.
The latest release version of the IMAP toolkit is always
available at ftp://ftp.cac.washington.edu/mail/imap.tar.Z
_________________________________________________________________
5.4 I see all these strcpy() and sprintf() calls, those are unsafe,
aren't they?
Yes and no.
It can be unsafe to do these calls if you do not know that the
string being written will fit in the buffer. However, they are
perfectly safe if you do know that.
Beware of programmers who advocate doing a brute-force change
of all instances of
strcpy (s,t);
to
strncpy (s,t,n)[n] = '\0';
and similar measures in the name of "fixing all possible buffer
overflows."
There are examples in which a security bug was introduced
because of this type of "fix", due to the programmer using the
wrong value for n. In one case, the programmer thought that n
was larger than it actually was, causing a NUL to be written
out of the buffer; in another, n was too small, and a security
credential was truncated.
What is particularly ironic was that in both cases, the
original strcpy() was safe, because the size of the source
string was known to be safe.
With all this in mind, the software has been inspected, and it
is believed that all places where buffer overflows can happen
have been fixed. The strcpy()s that are still are in the code
occur after a size check was done in some other way.
Note that the common C idiom of
*s++ = c;
is just as vulnerable to buffer overflows. You can't cure
buffer overflows by outlawing certain functions, nor is it
desirable to do so; sometimes operations like strcpy()
translate into fast machine instructions for better
performance.
Nothing replaces careful study of code. That's how the bad guys
find bugs. Security is not accomplished by means of brute-force
shortcuts.
_________________________________________________________________
5.5 Those /tmp lock files are protected 666, is that really right?
Yes. Shared mailboxes won't work otherwise. Also, you get into
accidental denial of service problems with old lock files left
lying around; this happens fairly frequently.
The deliberate mischief that can be caused by fiddling with the
lock files is small-scale; harassment level at most. There are
many -- and much more effective -- other ways of harassing
another user on UNIX. It's usually not difficult to determine
the culprit.
Before worrying about deliberate mischief, worry first about
things happening by accident!
_________________________________________________________________
6. Why Did You Do This Strange Thing? Questions
_________________________________________________________________
6.1 Why don't you use GNU autoconfig / automake / autoblurdybloop?
Autoconfig et al are not available on all the platforms where
the IMAP toolkit is supported; and do not work correctly on
some of the platforms where they do exist. Furthermore, these
programs add another layer of complexity to an already complex
process.
Coaxing software that uses autoconfig to build properly on
platforms which were not specifically considered by that
software wastes an inordinate amount of time. When (not if)
autoconfig fails to do the right thing, the result is an
inpenetrable morass to untangle in order to find the problem
and fix it.
The concept behind autoconfig is good, but the execution is
flawed. It rarely does the right thing on a platform that
wasn't specifically considered. Human life is too short to
debug autoconfig problems, especially since the current
mechanism is so much easier.
_________________________________________________________________
6.2 Why do you insist upon a build with -g? Doesn't it waste disk and
memory space?
From time to time a submitted port has snuck in without -g.
This has always ended up causing problems. There are only two
valid excuses for not using -g in a port:
+ The compiler does not support -g
+ An alternate form of -g is needed with optimization, e.g.
-g3.
There will be no new ports added without -g (or a suitable
alternative) being set.
-g has not been arbitrarily added to the ports which do not
currently have it because we don't know if doing so would break
the build. However, any support issues with one of those port
will lead to the correct -g setting being determined and
permanently added.
Processors are fast enough (and disk space is cheap enough)
that -g should be automatic in all compilers with no way of
turning it off, and /bin/strip should be a symlink to
/bin/true. Human life is too short to deal with binaries built
without -g. Such binaries should be a bad memory of the days of
KIPS processors and disks that costs several dollars per
kilobyte.
_________________________________________________________________
6.3 Why don't you make c-client a shared library?
All too often, shared libraries create far more problems than
they solve.
Remember that you only gain the benefit of a shared library
when there are multiple applications which use that shared
library. Even without shared libraries, on most modern
operating systems (and many ancient ones too!) applications
will share their text segments between across multiple
processes running the same application. This means that if your
system only runs one application (e.g. imapd) that uses the
c-client library, then you gain no benefit from making c-client
a shared library even if it has 100 imapd processes. You will,
however suffer added complexity.
If you have a server system that just runs imapd and ipop3d,
then making c-client a shared library will save just one copy
of c-client no matter how many IMAP/POP3 processes are running.
The problem with shared libraries is that you have to keep
around a copy of the library every time something changes in
the library that would affect the interface the library
presents to the application. So, you end up having many copies
of the same shared library.
If you don't keep multiple copies of the shared library, then
one of two things happens. If there was proper versioning, then
you'll get a message such as "cannot open shared object file"
or "minor versions don't match" and the application won't run.
Otherwise, the application will run, but will fail in
mysterious ways.
Several sites and third-party distributors have modified the
c-client makefile in order to make c-client be a shared
library. When (not if) a c-client based application fails in
mysterious ways because of a library compatibility problem, the
result is a bug report. A lot of time and effort ends up
getting wasted investigating such bug reports.
Memory is so cheap these days that it's not worth it. Human
life is too short to deal with shared library compatibility
problems.
_________________________________________________________________
6.4 Why don't you use iconv() for internationalization support?
iconv() is not ubiquitous enough.
_________________________________________________________________
6.5 Why is the IMAP server connected to the home directory by default?
The IMAP server has no way of knowing what you might call
"mail" as opposed to "some other file"; in fact, you can use
IMAP to access any file.
The IMAP server also doesn't know whether your preferred
subdirectory for mailbox files is "mail/", ".mail/", "Mail/",
"Mailboxes/", or any of a zillion other possibilities. If one
such name were chosen, it would undoubtably anger the partisans
of all the other names.
It is possible to modify the software so that the default
connected directory is someplace else. Please read the file
CONFIG for discussion of this and other issues.
_________________________________________________________________
6.6 I have a Windows system. Why isn't the server plug and play for
me?
There is no standard for how mail is stored on Windows; nor a
single standard SMTP server. The closest to either would be the
SMTP server in Microsoft's IIS.
So there's no default by which to make assumptions. As the
software is set up, it assumes that the each user has an
Windows login account and private home directory, and that mail
is stored on that home directory as files in one of the popular
UNIX formats. It also assumes that there is some tool
equivalent to inetd on UNIX that does the TCP/IP listening and
server startup.
Basically, unless you're an email software hacker, you probably
want to look elsewhere if you want IMAP/POP servers for
Windows.
_________________________________________________________________
6.7 I looked at the UNIX SSL code and saw that you have the SSL data
payload size set to 8192 bytes. SSL allows 16K; why aren't you using
the full size?
This is to avoid an interoperability problem with:
+ PC IMAP clients that use Microsoft's SChannel.DLL (SSPI) for
SSL support
+ Microsoft Exchange server (which also uses SChannel).
SChannel has a bug that makes it think that the maximum SSL
data payload size is 16379 bytes -- 5 bytes too small. Thus,
c-client has to make sure that it never transmits full sized
SSL packets.
The reason for using 8K (as opposed to, say, 16379 bytes, or
15K, or...) is that it corresponds with the TCP buffer size
that the software uses elsewhere for input; there's a slight
performance benefit to having the two sizes correspond or at
least be a multiple of each other. Also, it keeps the size as a
power of two, which might be significant on some platforms.
There wasn't a significant difference that we could measure
between 8K and 15K.
Microsoft has developed a hotfix for this bug. Look up MSKB
article number 300562. Contrary to the article text which
implies that this is a Pine issue, this bug also affects
Microsoft Exchange server with any client that transmits
full-sized SSL payloads.
_________________________________________________________________
6.8 Why is an mh format INBOX called #mhinbox instead of just INBOX?
It's a long story. In brief, the mh format driver is less
functional than any of the other drivers. It turned out that
there were some users (including high-level administrators) who
tried mh years ago and no longer use it, but still had an mh
profile left behind.
When the mh driver used INBOX, it would see the mh profile, and
proceed to move the user's INBOX into the mh format INBOX. This
caused considerable confusion as some things stopped working.
_________________________________________________________________
6.9 Why don't you support the maildir format?
It is technically difficult to support maildir in IMAP while
maintaining acceptable performance, robustness, following the
requirements of the IMAP protocol specification, and following
the requirements of maildir.
No one has succeeded in accomplishing all four together. The
various maildir drivers offered as patches all have these
problems. The problem is exacerbated because this
implementation supports multiple formats; consequently this
implementation can't make any performance shortcuts by assuming
that all the world is maildir.
We can't do a better job than the maildir fan community has
done with their maildir drivers. Similarly, if the maildir fan
community provides the maildir driver, they take on the
responsibility for answering maildir-specific support
questions. This is as it should be, and that is why maildir
support is left to the maildir fan community.
_________________________________________________________________
6.10 Why don't you support the Cyrus format?
There's no point to doing so. An implementation which supports
multiple formats will never do as well as one which is
optimized to support one single format.
If you want to use Cyrus mailbox format, you should use the
Cyrus server, which is the native implementation of that format
and is specifically optimized for that format. That's also why
Cyrus doesn't implement any other format.
_________________________________________________________________
6.11 Why is it creating extra forks on my SVR4 system?
This is because your system only has fcntl() style locking and
not flock() style locking. fcntl() locking has a design flaw
that causes a close() to release any locks made by that process
on the file opened on that file descriptor, even if the lock
was made on a different file descriptor.
This design flaw causes unexpected loss of lock, and consequent
mailbox corruption. The workaround is to do certain "dangerous
operations" in another fork, thus avoiding doing a close() in
the vulnerable fork.
The best way to solve this problem is to upgrade your SVR4
(Solaris, AIX, HP-UX, SGI) or OSF/1 system to a more advanced
operating system, such as Linux or BSD. These more advanced
operating systems have fcntl() locking for compatibility with
SVR4, but also have flock() locking.
Beware of certain SVR4 systems, such as AIX, which have an
"flock()" function in their C library that is just a jacket
that does an fcntl() lock. This is not a true flock(), and has
the same design flaw as fcntl().
_________________________________________________________________
6.12 Why are you so fussy about the date/time format in the internal
"From " line in traditional UNIX mailbox files? My other mail program
just considers every line that starts with "From " to be the start of
the message.
You just answered your own question. If any line that starts
with "From " is treated as the start of a message, then every
message text line which starts with "From " has to be quoted
(typically by prefixing a ">" character). People complain about
this -- "why did a > get stuck in my message?"
So, good mail reading software only considers a line to be a
"From " line if it follows the actual specification for a
"From " line. This means, among other things, that the day of
week is fixed-format: "May 14", but "May 7" (note the extra
space) as opposed to "May 7". ctime() format for the date is
the most common, although POSIX also allows a numeric timezone
after the year. For compatibility with ancient software, the
seconds are optional, the timezone may appear before the year,
the old 3-letter timezones are also permitted, and "remote from
xxx" may appear after the whole thing.
Unfortunately, some software written by novices use other
formats. The most common error is to have a variable-width day
of month, perhaps in the erroneous belief that RFC 2822 (or RFC
822) defines the format of the date/time in the "From " line
(it doesn't; no RFC describes internal formats). I've seen a
few other goofs, such as a single-digit second, but these are
less common.
If you are writing your own software that writes mailbox files,
and you really aren't all that savvy with all the ins and outs
and ancient history, you should seriously consider using the
c-client library (e.g. routine mail_append()) instead of doing
the file writes yourself. If you must do it yourself, use
ctime(), as in:
fprintf (mbx,"From %s@%h %s",user,host,ctime (time (0)));
rather than try to figure out a good format yourself. ctime()
is the most traditional format and nobody will flame you for
using it.
_________________________________________________________________
6.13 Why is traditional UNIX format the default format?
Compatibility with the past 30 or so years of UNIX history.
This server is the only one that completely interoperates with
legacy UNIX mail tools.
_________________________________________________________________
6.14 Why do you write this "DON'T DELETE THIS MESSAGE -- FOLDER
INTERNAL DATA" message at the start of traditional UNIX and MMDF
format mailboxes?
This pseudo-message serves two purposes.
First, it establishes the mailbox format even when the mailbox
has no messages. Otherwise, a mailbox with no messages is a
zero-byte file, which could be one of several formats.
Second, it holds mailbox metadata used by IMAP: the UID
validity, the last assigned UID, and mailbox keywords. Without
this metadata, which must be preserved even when the mailbox
has no messages, the traditional UNIX format wouldn't be able
to support the full capabilities of IMAP.
_________________________________________________________________
6.15 Why don't you stash the mailbox metadata in the first real
message of the mailbox instead of writing this fake FOLDER INTERNAL
DATA message?
In fact, that is what is done if the mailbox is non-empty and
does not already have a FOLDER INTERNAL DATA message.
One problem with doing that is that if some external program
removes the first message, the metadata is lost and must be
recreated, thus losing any prior UID or keyword list status
that IMAP clients may depend upon.
Another problem is that this doesn't help if the last message
is deleted. This will result in an empty mailbox, and the
necessity to create a FOLDER INTERNAL DATA message.
_________________________________________________________________
6.16 Why aren't "dual-use" mailboxes the default?
Compatibility with the past 30 or so years of UNIX history, not
to mention compatibility with user expectations when using
shell tools.
_________________________________________________________________
6.17 Why do you use ucbcc to build on Solaris?
It is a long, long story about why cc is set to ucbcc. You need
to invoke the C compiler so that it links with the SVR4
libraries and not the BSD libraries, otherwise readdir() will
return the wrong information.
Of all the names in the most common path, ucbcc is the only
name to be found (on /usr/ccs/bin) that points to a suitable
compiler. cc is likely to be /usr/ucb/cc which is absolutely
not the compiler that you want. The real SVR4 cc is probably
something like /opt/SUNWspro/bin/cc which is rarely in anyone's
path by default.
ucbcc is probably a link to acc, e.g.
/opt/SUNWspro/SC4.0/bin/acc, and is the UCB C compiler using
the SVR4 libraries.
If ucbcc isn't on your system, then punt on the SUN C compiler
and use gcc instead (the gso port instead of the sol port).
If, in spite of all the above warnings, you choose to change
"ucbcc" to "cc", you will probably find that the -O2 needs to
be changed to -O. If you don't get any error messages with -O2,
that's a pretty good indicator that you goofed and are running
the compiler that will link with the BSD libraries.
To recap:
+ The sol port is designed to be built using the UCB compiler
using the SVR4 libraries. This compiler is "ucbcc", which is
lunk to acc. You use -O2 as one of the CFLAGS.
+ If you build the sol port with the UCB compiler using the BSD
libraries, you will get no error messages but you will get
bad binaries (the most obvious symptom is dropping the first
two characters return filenames from the imapd LIST command.
This compiler also uses -O2, and is very often what the user
gets from "cc". BEWARE
+ If you build the sol port with the real SVR4 compiler, which
is often hidden away or unavailable on many systems, then you
will get errors from -O2 and you need to change that to -O.
But you will get a good binary. However, you should try it
with -O2 first, to make sure that you got this compiler and
not the UCB compiler using BSD libraries.
_________________________________________________________________
6.18 Why should I care about some old system with BSD libraries? cc is
the right thing on my Solaris system!
Because there still are sites that use such systems. On those
systems, the assumption that "cc" does the right thing will
lead to corrupt binaries with no error message or other warning
that anything is amiss.
Too many sites have fallen victim to this problem.
_________________________________________________________________
6.19 Why do you insist upon writing .lock files in the spool
directory?
Compatibility with the past 30 years of UNIX software which
deals with the spool directory, especially software which
delivers mail. Otherwise, it is possible to lose mail.
_________________________________________________________________
6.20 Why should I care about compatibility with the past?
This is one of those questions in which the answer never
convinces those who ask it. Somehow, everybody who ever asks
this question ends up answering it for themselves as they get
older, with the very answer that they rejected years earlier.
_________________________________________________________________
7. Problems and Annoyances
_________________________________________________________________
7.1 Help! My INBOX is empty! What happened to my messages?
If you are seeing "0 messages" when you open INBOX and you know
you have messages there (and perhaps have looked at your mail
spool file and see that messages are there), then probably
there is something wrong with the very first line of your mail
spool file. Make sure that the first five bytes of the file are
"From ", followed by an email address and a date/time in
ctime() format, e.g.:
From fred@foo.bar Mon May 7 20:54:30 2001
_________________________________________________________________
7.2 Help! All my messages in a non-INBOX mailbox have been
concatenated into one message which claims to be from me and has a
subject of the file name of the mailbox! What's going on?
Something wrong with the very first line of the mailbox. Make
sure that the first five bytes of the file are "From ",
followed by an email address and a date/time in ctime() format,
e.g.:
From fred@foo.bar Mon May 7 20:54:30 2001
_________________________________________________________________
7.3 Why do I get the message: CREATE failed: Can't create mailbox node
xxxxxxxxx: File exists and how do I fix it?
See the answer to the Are hierarchical mailboxes supported?
question.
_________________________________________________________________
7.4 Why can't I log in to the server? The user name and password are
right!
There are a myriad number of possible answers to this question.
The only way to say for sure what is wrong is run the server
under a debugger such as gdb while root (yes, you must be root)
with a breakpoint at routines checkpw() and loginpw(), then
single-step until you see which test rejected you. The server
isn't going to give any error messages other than "login
failed" in the name of not giving out any unnecessary
information to unauthorized individuals.
Here are some of the more common reasons why login may fail:
+ You didn't really give the correct user name and/or password.
+ Your client doesn't send the LOGIN command correctly; for
example, IMAP2 clients won't send a password containing a "*"
correctly to an IMAP4 server.
+ If you have set up a CRAM-MD5 database, remember that the
password used is the one in the CRAM-MD5 database, and
furthermore that there must also be an entry in /etc/passwd
(but the /etc/passwd password is not used).
+ If you are using PAM, have you created a service file for the
server in /etc/pam.d?
+ If you are using shadow passwords, have you used an
appropriate port when building? In particular, note that
"lnx" is for Linux systems without shadow passwords; you
probably want "slx" or "lnp" instead.
+ If your system has account or password expirations, check to
see that the expiration date hasn't passed.
+ You can't log in as root or any other UID 0 user. This is for
your own safety, not to mention the fact that the servers use
UID 0 as meaning "not logged in".
_________________________________________________________________
7.5 Help! My load average is soaring and I see hundreds of POP and
IMAP servers, many logged in as the same user!
Certain inferior losing GUI mail reading programs have a
"synchronize all mailboxes at startup" (IMAP) or "check for new
mail every second" (POP) feature which causes a rapid and
unchecked spawning of servers.
This is not a problem in the server; the client is really
asking for all those server sessions. Unfortunately, there
isn't much that the POP and IMAP servers can do about it; they
don't spawned themselves.
Some sites have added code to record the number of server
sessions spawned per user per hour, and disable login for a
user who has exceeded a predetermined rate. This doesn't stop
the servers from being spawned; it just means that a server
session will commit suicide a bit faster.
Another possibility is to detect excessive server spawning
activity at the level where the server is spawned, which would
be inetd or possibly tcpd. The problem here is that this is a
hard time to quantify. 50 sessions in a minute from a
multi-user timesharing system may be perfectly alright, whereas
10 sessions a minute from a PC may be too much.
The real solution is to fix the client configuration, by
disabling those evil features. Also tell the vendors of those
clients how you feel about distributing denial-of-service
attack tools in the guise of mail reading programs.
_________________________________________________________________
7.6 Why does mail disappear even though I set "keep mail on server"?
7.7 Why do I get the message Moved ##### bytes of new mail to
/home/user/mbox from /var/spool/mail/user and why did this happen?
This is probably caused by the mbox driver. If the file "mbox"
exists on the user's home directory and is in UNIX mailbox
format, then when INBOX is opened this file will be selected as
INBOX instead of the mail spool file. Messages will be
automatically transferred from the mail spool file into the
mbox file.
To disable this behavior, delete "mbox" from the EXTRADRIVERS
list in the top-level Makefile and rebuild. Note that if you do
this, users won't be able to access the messages that have
already been moved to mbox unless they open mbox instead of
INBOX.
_________________________________________________________________
7.8 Why isn't it showing the local host name as a fully-qualified
domain name?
7.9 Why is the local host name in the From/Sender/Message-ID headers
of outgoing mail not coming out as a fully-qualified domain name?
Your UNIX system is misconfigured. The entry for your system in
/etc/hosts must have the fully-qualified domain name first,
e.g.
105.69.1.234 myserver.example.com myserver
A common mistake of novice system administrators is to have the
short name first, e.g.
105.69.1.234 myserver myserver.example.com
or to omit the fully qualified domain name entirely, e.g.
105.69.1.234 myserver
The result of this is that when the IMAP toolkit does a
gethostbyname() call to get the fully-qualified domain name, it
would get "myserver" instead of "myserver.example.com".
On some systems, a configuration file (typically named
/etc/svc.conf, /etc/netsvc.conf, or /etc/nsswitch.conf) can be
used to configure the system to use the domain name system
(DNS) instead of /etc/hosts, so it doesn't matter if /etc/hosts
is misconfigured.
Check the man pages for gethostbyname, hosts, svc, and/or
netsvc for more information.
Unfortunately, certain vendors, most notably SUN, have failed
to make this clear in their documentation. Most of SUN's
documentation assumes a corporate network that is not connected
to the Internet.
net.folklore once (late 1980s) held that the proper procedure
was to append the results of getdomainname() to the name
returned by gethostname(), and some versions of sendmail
configuration files were distributed that did this. This was
incorrect; the string returned from getdomainname() is the
Yellow Pages (a.k.a NIS) domain name, which is a completely
different (albeit unfortunately named) entity from an Internet
domain. These were often fortuitously the same string, except
when they weren't. Frequently, this would result in host names
with spuriously doubled domain names, e.g.
myserver.example.com.example.com
This practice has been thoroughly discredited for many years,
but folklore dies hard.
_________________________________________________________________
7.10 What does the message: Mailbox vulnerable - directory
/var/spool/mail must have 1777 protection mean? How can I fix this?
In order to update a mailbox in the default UNIX format, it is
necessary to create a lock file to prevent the mailer from
delivering mail while an update is in progress. Some systems
use a directory protection of 775, requiring that all mail
handling programs be setgid mail; or of 755, requiring that all
mail handling programs be setuid root.
The IMAP toolkit does not run with any special privileges, and
I plan to keep it that way. It is antithetical to the concept
of a toolkit if users can't write their own programs to use it.
Also, I've had enough bad experiences with security bugs while
running privileged; the IMAP and POP servers have to be root
when not logged in, in order to be able to log themselves in. I
don't want to go any deeper down that slippery slope.
Directory protection 1777 is secure enough on most well-managed
systems. If you can't trust your users with a 1777 mail spool
(petty harassment is about the limit of the abuse exposure),
then you have much worse problems then that.
If you absolutely insist upon requiring privileges to create a
lock file, external file locking can be done via a setgid mail
program named /etc/mlock (this is defined by LOCKPGM in the
c-client Makefile). If the toolkit is unable to create a
<...mailbox...>.lock file in the directory by itself, it will
try to call mlock to do it. I do not recommend doing this for
performance reasons.
A sample mlock program is included as part of imap-2007. We
have tried to make this sample program secure, but it has not
been thoroughly audited.
_________________________________________________________________
7.11 What does the message: Mailbox is open by another process, access
is readonly mean? How do I fix this?
A problem occurred in applying a lock to a /tmp lock file.
Either some other program has the mailbox open and won't
relenquish it, or something is wrong with the protection of
/tmp or the lock.
Make sure that the /tmp directory is protected 1777. Some
security scripts incorrectly set the protection of the /tmp
directory to 775, which disables /tmp for all non-privileged
programs.
_________________________________________________________________
7.12 What does the message: Can't get write access to mailbox, access
is readonly mean?
The mailbox file is write-protected against you.
_________________________________________________________________
7.13 I set my POP3 client to "delete messages from server" but they
never get deleted. What is wrong?
Make sure that your mailbox is not read-only: that the mailbox
is owned by you and write enabled (protection 0600), and that
the /tmp directory is longer world-writeable. /tmp must be
world-writeable because lots of applications use it for scratch
space. To fix this, do
chmod 1777 /tmp
as root.
Make sure that your POP3 client issues a QUIT command when it
finishes. The POP3 protocol specifies that deletions are
discarded unless a proper QUIT is done.
Make sure that you are not opening multiple POP3 sessions to
the same mailbox. It is a requirement of the POP3 protocol than
only one POP3 session be in effect to a mailbox at a time,
however some, poorly-written POP3 clients violate this. Also,
some background "check for new mail" tasks also cause a
violation. See the answer to the What does the syslog message:
Killed (lost mailbox lock) user=... host=... mean? question for
more details.
_________________________________________________________________
7.14 What do messages such as:
Message ... UID ... already has UID ...
Message ... UID ... less than ...
Message ... UID ... greater than last ...
Invalid UID ... in message ..., rebuilding UIDs
mean?
Something happened to corrupt the unique identifier regime in
the mailbox. In traditional UNIX-format mailboxes, this can
happen if the user deleted the "DO NOT DELETE" internal
message.
This problem is relatively harmless; a new valid unique
identifier regime will be created. The main effect is that any
references to the old UIDs will no longer be useful.
So, unless it is a chronic problem or you feel like debugging,
you can safely ignore these messages.
_________________________________________________________________
7.15 What do the error messages:
Unable to read internal header at ...
Unable to find CRLF at ...
Unable to parse internal header at ...
Unable to parse message date at ...
Unable to parse message flags at ...
Unable to parse message UID at ...
Unable to parse message size at ...
Last message (at ... ) runs past end of file ...
mean? I am using mbx format.
The mbx-format mailbox is corrupted and needs to be repaired.
You should make an effort to find out why the corruption
happened. Was there an obvious system problem (crash or disk
failure)? Did the user accidentally access the file via NFS?
Mailboxes don't get corrupted by themselves; something caused
the problem.
Some people have developed automated scripts, but if you're
comfortable using emacs it's pretty easy to fix it manually. Do
not use vi or any other editor unless you are certain that
editor can handle binary!!!
If you are not comfortable with emacs, or if the file is too
large to read with emacs, see the "step-by-step" technique
later on for another way of doing it.
After the word "at" in the error message is the byte position
it got to when it got unhappy with the file, e.g. if you see:
Unable to parse internal header at 43921: ne bombastic blurdybloop
The problem occurs at the 43,931 byte in the file. That's the
point you need to fix. c-client is expecting an internal header
at that byte number, looking something like:
6-Jan-1998 17:42:24 -0800,1045;000000100001-00000001
The format of this internal line is:
dd-mmm-yyyy hh:mm:ss +zzzz,ssss;ffffffffFFFF-UUUUUUUU
The only thing that is variable is the "ssss" field, it can be
as many digits as needed. All other fields (inluding the "dd")
are fixed width. So, the easiest thing to do is to look forward
in the file for the next internal header, and delete everything
from the error point to that internal header.
Here's what to do if you want to be smarter and do a little bit
more work. Generally, you're in the middle of a message, and
there's nothing wrong with that message. The problem happened
in the *previous* message. So, search back to the previous
internal header. Now, remember that "ssss" field? That's the
size of that message.
Mark where you are in the file, move the cursor to the line
after the internal header, and skip that many bytes ("ssss")
forward. If you're at the point of the error in the file, then
that message is corrupt. If you're at a different point, then
perhaps the previous message is corrupt and has a too long size
count that "ate" into this message.
Basically, what you need to do is make sure that all those size
counts are right, and that moving "ssss" bytes from the line
after the internal header will land you at another internal
header.
Usually, once you know what you're looking at, it's pretty easy
to work out the corruption, and the best remedial action.
Repair scripts will make the problem go away but may not always
do the smartest/best salvage of the user's data. Manual repair
is more flexible and usually preferable.
Here is a step-by-step technique for fixing corrupt mbx files
that's a bit cruder than the procedure outlined above, but
works for any size file.
In this example, suppose that the corrupt file is INBOX, the
error message is
Unable to find CRLF at 132551754
and the size of the INBOX file is 132867870 bytes.
The first step is to split the mailbox file at the point of the
error:
+ Rename the INBOX file to some other name, such as INBOX.bad.
+ Copy the first 132,551,754 bytes of INBOX.bad to another
file, such as INBOX.new.
+ Extract the trailing 316,116 bytes (132867870-132551754) of
INBOX.bad into another file, such as INBOX.tail.
+ You no longer need INBOX.bad. Delete it.
In other words, use the number from the "Unable to find CRLF
at" as the point to split INBOX into two new files, INBOX.new
and INBOX.tail.
Now, remove the erroneous data:
+ Verify that you can open INBOX.new in IMAP or Pine.
+ The last message of INBOX.new is probably corrupted. Copy it
to another file, such as badmsg.1, then delete and expunge
that last message from INBOX.new
+ Locate the first occurance of text in INBOX.tail which looks
like an internal header, as described above.
+ Remove all the text which occurs prior to that point, and
place it into another file, such as badmsg.2. Note that in
the case of a single digit date, there is a leading space
which must not be removed (e.g. " 6-Nov-2001" not
"6-Nov-2001").
Reassemble the mailbox:
+ Append INBOX.tail to INBOX.new.
+ You no longer need INBOX.tail. Delete it.
+ Verify that you can open INBOX.new in IMAP or Pine.
Reinstall INBOX.new as INBOX:
+ Check to see if you have received any new messages while
repairing INBOX.
+ If you haven't received any new messages while repairing
INBOX, just rename INBOX.new to INBOX.
+ If you have received new messages, be sure to copy the new
messages from INBOX to INBOX.new before doing the rename.
You now have a working INBOX, as well as two files with
corrupted data (badmsg.1 and badmsg.2). There may be some
useful data in the two badmsg files that you might want to try
salvaging; otherwise you can delete the two badmsg files.
_________________________________________________________________
7.16 What do the syslog messages:
imap/tcp server failing (looping)
pop3/tcp server failing (looping)
mean? When it happens, the listed service shuts down. How can I fix
this?
The error message "server failing (looping), service
terminated" is not from either the IMAP or POP servers.
Instead, it comes from inetd, the daemon which listens for TCP
connections to a number of servers, including the IMAP and POP
servers.
inetd has a limit of 40 new server sessions per minute for any
particular service. If more than 40 sessions are initiated in a
minute, inetd will issue the "failing (looping), service
terminated" message and shut down the service for 10 minutes.
inetd does this to prevent system resource consumption by a
client which is spawning infinite numbers of servers. It should
be noted that this is a denial of service; however for some
systems the alternative is a crash which would be a worse
denial of service!
For larger server systems, the limit of 40 is much too low. The
limit was established many years ago when a system typically
only ran a few dozen servers.
On some versions of inetd, such as the one distributed with
most versions of Linux, you can modify the /etc/inetd.conf file
to have a larger number of servers by appending a period
followed by a number after the nowait word for the server
entry. For example, if your existing /etc/inetd.conf line
reads:
imap stream tcp nowait root /usr/etc/imapd imapd
try changing it to be:
imap stream tcp nowait.100 root /usr/etc/imapd imapd
Another example (using TCP wrappers):
imap stream tcp nowait root /usr/sbin/tcpd imapd
try changing it to be:
imap stream tcp nowait.100 root /usr/sbin/tcpd imapd
to increase the limit to 100 sessions/minute.
Before making this change, please read the information in "man
inetd" to determine whether or not your inetd has this feature.
If it does not, and you make this change, the likely outcome is
that you will disable IMAP service entirely.
Another way to fix this problem is to edit the inetd.c source
code (provided by your UNIX system vendor) to set higher
limits, rebuild inetd, install the new binary, and reboot your
system. This should only be done by a UNIX system expert. In
the inetd.c source code, the limits TOOMANY (normally 40) is
the maximum number of new server sessions permitted per minute,
and RETRYTIME (normally 600) is the number of seconds inetd
will shut down the server after it exceeds TOOMANY.
_________________________________________________________________
7.17 What does the syslog message: Mailbox lock file /tmp/.600.1df3
open failure: Permission denied mean?
This usually means that some "helpful" security script person
has protected /tmp so that it is no longer world-writeable.
/tmp must be world-writeable because lots of applications use
it for scratch space. To fix this, do
chmod 1777 /tmp
as root.
If that isn't the answer, check the protection of the named
file. If it is something other than 666, then either someone is
hacking or some "helpful" person modified the code to have a
different default lock file protection.
_________________________________________________________________
7.18 What do the syslog messages:
Command stream end of file, while reading line user=... host=...
Command stream end of file, while reading char user=... host=...
Command stream end of file, while writing text user=... host=...
mean?
This message occurs when the session is disconnected without a
proper LOGOUT (IMAP) or QUIT (POP) command being received by
the server first.
In many cases, this is perfectly normal; many client
implementations are impolite and do this. Some programmers
think this sort of rudeness is "more efficient".
The condition could, however, indicate a client or network
connectivity problem. The server has no way of knowing whether
there's a problem or just a rude client, so it issues this
message instead of a Logout.
Certain inferior losing clients disconnect abruptly after a
failed login, and instead of saying that the login failed, just
say that they can't access the mailbox. They then complain to
the system manager, who looks in the syslog and finds this
message. Not very helpful, eh? See the answer to the Why can't
I log in to the server? The user name and password are right!
question.
If the user isn't reporting a problem, you can probably ignore
this message.
_________________________________________________________________
7.19 Why did my POP or IMAP session suddenly disconnect? The syslog
has the message: Killed (lost mailbox lock) user=... host=...
This message only happens when either the traditional UNIX
mailbox format or MMDF format is in use. This format only
allows one session to have the mailbox open read/write at a
time.
The servers assume that if a second session attempts to open
the mailbox, that means that the first session is probably
owned by an abandoned client. The common scenario here is a
user who leaves his client running at the office, and then
tries to read his mail from home. Through an internal mechanism
called kiss of death, the second session requests the first
session to kill itself. When the first session receives the
"kiss of death", it issues the "Killed (lost mailbox lock)"
syslog message and terminates. The second session then seizes
read/write access, and becomes the new "first" session.
Certain poorly-designed clients routinely open multiple
sessions to the same mailbox; the users of those clients tend
to get this message a lot.
Another cause of this message is a background "check for new
mail" task which does its work by opening a POP session to
server every few seconds. They do this because POP doesn't have
a way to announce new mail.
The solution to both situations is to replace the client with a
good online IMAP client such as Pine. Life is too short to
waste on POP clients and poorly-designed IMAP clients.
_________________________________________________________________
7.20 Why does my IMAP client show all the files on the system,
recursively from the UNIX root directory?
7.21 Why does my IMAP client show all of my files, recursively from my
UNIX home directory?
A well-written client should only show one level of hierarchy
and then stop, awaiting explicit user action before going
lower. However, some poorly-designed clients will recursively
list all files, which may be a very long list (especially if
you have symbolic links to directories that create a loop in
the filesystem graph!).
This behavior has also been observed in some third-party
c-client drivers, including maildir drivers. Consequently, this
problem has even been observed in Pine. It is important to
understand that this is not a problem in Pine or c-client; it
is a problem in the third-party driver. A Pine built without
that third-party driver will not have this problem.
See also the answer to Why does my IMAP client show all my
files in my home directory?
_________________________________________________________________
7.22 Why does my IMAP client show that I have mailboxes named
"#mhinbox", "#mh", "#shared", "#ftp", "#news", and "#public"?
These are IMAP namespace names. They represent other
hierarchies in which messages may exist. These hierarchies may
not necessarily exist on a server, but the namespace name is
still in the namespace list in order to mark it as reserved.
A few poorly-designed clients display all namespace names as if
they were top-level mailboxes in a user's list of mailboxes,
whether or not they actually exist. This is a flaw in those
clients.
_________________________________________________________________
7.23 Why does my IMAP client show all my files in my home directory?
As distributed, the IMAP server is connected to your home
directory by default. It has no way of knowing what you might
call "mail" as opposed to "some other file"; in fact, you can
use IMAP to access any file.
Most clients have an option to configure your connected
directory on the IMAP server. For example, in Pine you can
specify this as the "Path" in your folder-collection, e.g.
Nickname : Secondary Folders
Server : imap.example.com
Path : mail/
View :
In this example, the user is connected to the "mail"
subdirectory of his home directory.
Other servers call this the "folder prefix" or similar term.
It is possible to modify the IMAP server so that all users are
automatically connected to some other directory, e.g. a
subdirectory of the user's home directory. Read the file CONFIG
for more details.
_________________________________________________________________
7.24 Why is there a long delay before I get connected to the IMAP or
POP server, no matter what client I use?
There are two common occurances of this problem:
+ You are running a system (e.g. certain versions of Linux)
which by default attempts to connect to an "IDENT" protocol
(port 113) server on your client. However, a firewall or NAT
box is blocking connections to that port, so the connection
attempt times out.
The IDENT protocol is a well-known bad idea that does not
deliver any real security but causes incredible problems. The
idea is that this will give the server a record of the user
name, or at least what some program listening on port 113
says is the user name. So, if somebody coming from port nnnnn
on a system does something bad, IDENT may give you the userid
of the bad guy.
The problem is, IDENT is only meaningful on a timesharing
system which has an administrator who is privileged and users
who are not. It is of no value on a personal system which has
no separate concept of "system administrator" vs.
"unprivileged user".
On either type of system, security-minded people either turn
IDENT off or replace it with an IDENT server that lies. Among
other things, IDENT gives spammers the ability to harvest
email addresses from anyone who connects to a web page.
This problem has been showing up quite frequently on systems
which use xinetd instead of inetd. Look for files named
/etc/xinetd.conf, /etc/xinetd.d/imapd, /etc/inetd.d/ipop2d,
and /etc/xinetd.d/ipop3d. In those files, look for lines
containing "USERID", e.g.
log_on_success += USERID
Hunt down such lines, and delete them ruthlessly from all
files in which they occur. Don't be shy about it.
+ The DNS is taking a long time to do a reverse DNS (PTR
record) lookup of the IP address of your client. This is a
problem in your DNS, which either you or you ISP need to
resolve. Ideally, the DNS should return the client's name;
but if it can't it should at least return an error quickly.
As you may have noticed, neither of these are actual problems
in the IMAP or POP servers; they are configuration issues with
either your system or your network infrastructure. If this is
all new to you, run (don't walk) to the nearest technical
bookstore and get yourself a good pedagogical text on system
administration for the type of system you are running.
_________________________________________________________________
7.25 Why is there a long delay in Pine or any other c-client based
application call before I get connected to the IMAP server? The hang
seems to be in the c-client mail_open() call. I don't have this
problem with any other IMAP client. There is no delay connecting to a
POP3 or NNTP server with mail_open().
By default, the c-client library attempts to make a connection
through rsh (and ssh, if you enable that). If the command:
rsh imapserver exec /etc/rimapd
(or ssh if that is enabled) returns with a "* PREAUTH"
response, it will use the resulting rsh session as the IMAP
session and not require an authentication step on the server.
Unfortunately, rsh has a design error that treats "TCP
connection refused" as "temporary failure, try again"; it
expects the "rsh not allowed" case to be implemented as a
successful connection followed by an error message and close
the connection.
It must be emphasized that this is a bug in rsh. It is not a
bug in the IMAP toolkit.
The use of rsh can be disabled in any the following ways:
+ You can disable it for this particular session by either:
o setting an explicit port number in the mailbox name,
e.g.
{imapserver.foo.com:143}INBOX
o using SSL (the /ssl switch)
+ You can disable rsh globally by setting the rsh timeout value
to 0 with the call:
mail_parameters (NIL,SET_RSHTIMEOUT,0);
_________________________________________________________________
7.26 Why does a message sometimes get split into two or more messages
on my SUN system?
This is caused by an interaction of two independent design
problems in SUN mail software. The first problem is that the
"forward message" option in SUN's mail tool program includes
the internal "From " header line in the text that it forwarded.
This internal header line is specific to traditional UNIX
mailbox files and is not suitable for use in forwarded
messages.
The second problem is that the mail delivery agent assumes that
mail reading programs will not use the traditional UNIX mailbox
format but instead an incompatible variant that depends upon a
Content-Length: message header. Content-Length is widely
recognized to have been a terrible mistake, and is no longer
recommended for use in mail (it is used in other facilities
that use MIME).
One symptom of the problem is that under certain circumstances,
a message may get broken up into several messages. I'm also
aware of security bugs caused by programs that foolishly trust
"Content-Length:" headers with evil values.
To fix the mailer on your system, edit your sendmail.cf to
change the Mlocal line to have the -E flag. A typical entry
will lool like:
Mlocal, P=/usr/lib/mail.local, F=flsSDFMmnPE, S=10, R=20,
A=mail.local -d $u
This fix will also work around the problem with mail tool,
because it will insert a ">" before the internal header line to
prevent it from being interpreted by mail reading software as
an internal header line.
_________________________________________________________________
7.27 Why did my POP or IMAP session suddenly disconnect? The syslog
has the message:
Autologout user=<...my user name...> host=<...my client system...>
This is a problem in your client.
In the case of IMAP, it failed to communicate with the IMAP
server for over 30 minutes; in the case of POP, it failed to
communicate with the POP server for over 10 minutes.
_________________________________________________________________
7.28 What does the UNIX error message: TLS/SSL failure: myserver: SSL
negotiation failed mean?
7.29 What does the PC error message: TLS/SSL failure: myserver:
Unexpected TCP input disconnect mean?
This usually means that an attempt to negotiate TLS encryption
via the STARTTLS command failed, because the server advertises
STARTTLS functionality, but doesn't actually have it (e.g.
because no certificates are installed).
Use the /notls option in the mailbox name to disable TLS
negotiation.
_________________________________________________________________
7.30 What does the error message: TLS/SSL failure: myserver: Server
name does not match certificate mean?
An SSL or TLS session encryption failed because the server name
in the server's certificate does not match the name that you
gave it. This could indicate that the server is not really the
system you think that it is, but can be also be called if you
gave a nickname for the server or name that was not
fully-qualified. You must use the fully-qualified domain name
for the server in order to validate its certificate
Use the /novalidate-cert option in the mailbox name to disable
validation of the certificate.
_________________________________________________________________
7.31 What does the UNIX error message: TLS/SSL failure: myserver:
self-signed certificate mean?
7.32 What does the PC error message: TLS/SSL failure: myserver:
Self-signed certificate or untrusted authority mean?
An SSL or TLS session encryption failed because your server's
certificate is "self-signed"; that is, it is not signed by any
Certificate Authority (CA) and thus can not be validated. A
CA-signed certificate costs money, and some smaller sites
either don't want to pay for it or haven't gotten one yet. The
bad part about this is that this means there is no guarantee
that the server is really the system you think that it is.
Use the /novalidate-cert option in the mailbox name to disable
validation of the certificate.
_________________________________________________________________
7.33 What does the UNIX error message: TLS/SSL failure: myserver:
unable to get local issuer certificate mean?
An SSL or TLS session encryption failed because your system
does not have the Certificate Authority (CA) certificates
installed on OpenSSL's certificates directory. On most systems,
this directory is /usr/local/ssl/certs). As a result, it is not
possible to validate the server's certificate.
If CA certificates are properly installed, you should see
factory.pem and about a dozen other .pem names such as
thawteCb.pem.
As a workaround, you can use the /novalidate-cert option in the
mailbox name to disable validation of the certificate; however,
note that you are then vulnerable to various security attacks
by bad guys.
The correct fix is to copy all the files from the certs/
directory in the OpenSSL distribution to the
/usr/local/ssl/certs (or whatever) directory. Note that you
need to do this after building OpenSSL, because the OpenSSL
build creates a number of needed symbolic links. For some
bizarre reason, the OpenSSL "make install" doesn't do this for
you, so you must do it manually.
_________________________________________________________________
7.34 Why does reading certain messages hang when using Netscape? It
works fine with Pine!
There are two possible causes.
Check the mail syslog. If you see the message "Killed (lost
mailbox lock)" for the impacted user(s), read the FAQ entry
regarding that message.
Check the affected mailbox to see if there are embedded NUL
characters in the message. NULs in message texts are a
technical violation of both the message format and IMAP
specifications. Most clients don't care, but apparently
Netscape does.
You can work around this by rebuilding imapd with the
NETSCAPE_BRAIN_DAMAGE option set (see src/imapd/Makefile); this
will cause imapd to convert all NULs to 0x80 characters. A
better solution is to enable the feature in your MTA to
MIME-convert messages with binary content. See the
documentation for your MTA for how to do this.
_________________________________________________________________
7.35 Why does Netscape say that there's a problem with the IMAP server
and that I should "Contact your mail server administrator."?
Certain versions of Netscape do this when you click the Manage
Mail button, which uses an undocumented feature of Netscape's
proprietary IMAP server.
You can work around this by rebuilding imapd with the
NETSCAPE_BRAIN_DAMAGE option set (see src/imapd/Makefile) to a
URL that points either to an alternative IMAP client (e.g.
Pine) or perhaps to a homebrew mail account management page.
_________________________________________________________________
7.36 Why is one user creating huge numbers of IMAP or POP server
sessions?
The user is probably using Outlook Express, Eudora, or a
similar program. See the answer to the Help! My load average is
soaring and I see hundreds of POP and IMAP servers, many logged
in as the same user! question.
_________________________________________________________________
7.37 Why don't I get any new mail notifications from Outlook Express
or Outlook after a while?
This is a known bug in Outlook Express. Microsoft is aware of
the problem and its cause. They have informed us that they do
not have any plans to fix it at the present time.
The problem is also reported in Outlook 2000, but not verified.
Outlook Express uses the IMAP IDLE command to avoid having to
"ping" the server every few minutes for new mail.
Unfortunately, Outlook Express overlooks the part in the IDLE
specification which requires that a client terminate and
restart the IDLE before the IMAP 30 minute inactivity
autologout timer triggers.
When this happens, Outlook Express displays "Not connected" at
the bottom of the window. Since it's no longer connected to the
IMAP server, it isn't going to notice any new mail.
As soon as the user does anything that would cause an IMAP
operation, Outlook Express will reconnect and new mail will
flow again. If the user does something that causes an IMAP
operation at least every 29 minutes, the problem won't happen.
Modern versions of imapd attempt to work around the problem by
automatically reporting fake new mail after 29 minutes. This
causes Outlook Express to exit the IDLE state; as soon as this
happens imapd revokes the fake new mail. As long as this
behavior isn't known to cause problems with other clients, this
workaround will remain in imapd.
_________________________________________________________________
7.38 Why don't I get any new mail notifications from Entourage?
This is a known bug in Entourage.
You built an older version of imapd with the
MICROSOFT_BRAIN_DAMAGE option set, in order to disable support
for the IDLE command. However, Entourage won't get new mail
unless IDLE command support exists.
Note: the MICROSOFT_BRAIN_DAMAGE option no longer exists in
modern versions, as the Outlook Express problem which it
attempted to solve has been worked around in another way.
_________________________________________________________________
7.39 Why doesn't Entourage work at all?
It's hard to know. Entourage breaks almost every rule in the
book for IMAP. It is highly instructive to do a packet trace on
Entourage, as an example of how not to use IMAP. It does things
like STATUS (MESSAGES) on the currently selected mailbox and
re-fetching the same static data over and over again.
It seems that every time we understand what it is doing wrong
in Entourage and come up with a workaround, we learn about
something else that's broken.
Try building imapd with the ENTOURAGE_BRAIN_DAMAGE option set,
in order to disable the diagnostic that occurs when doing
STATUS on the currently selected mailbox.
_________________________________________________________________
7.40 Why doesn't Netscape Notify (NSNOTIFY.EXE) work at all?
This is a bug in NSNOTIFY; it doesn't handle unsolicited data
from the server correctly.
Fortunately, there is no reason to use this program with IMAP;
NSNOTIFY is a polling program to let you know when new mail has
appeared in your maildrop. This is necessary with POP; but
since IMAP dynamically announces new mail in the session you're
better off (and will actually cause less load on the server!)
keeping your mail reading program's IMAP session open and let
IMAP do the notifying for you.
Consequently, the recommended fix for the NSNOTIFY problem is
to delete the NSNOTIFY binary.
_________________________________________________________________
7.41 Why can't I connect via SSL to Eudora? It says the connection has
been broken, and in the server syslogs I see "Command stream end of
file".
There is a report that you can fix the problem by going into
Eudora's advanced network configuration menu and increasing the
network buffer size to 8192.
_________________________________________________________________
7.42 Sheesh. Aren't there any good IMAP clients out there?
Yes!
Pine is a wonderful client. It's fast, it uses IMAP well, and
it generates text mail (life is too short to waste on HTML
mail). Also, there are some really wonderful things in progress
in the Pine world.
There are some good GUI clients out there, mostly from smaller
vendors. Without naming names, look for the vendors who are
active in the IMAP protocol development community, and their
products.
Netscape, Eudora, and Outlook can be configured with enough
effort to be good citizens and work well for users, but they
can also be badly misconfigured, and often the misconfiguration
is the default.
_________________________________________________________________
7.43 But wait! PC Pine (or other PC program build with c-client)
crashes with the message incomplete SecBuffer exceeds maximum buffer
size when I use SSL connections. This is a bug in c-client, right?
It's a bug in the Microsoft SChannel.DLL, which implements SSL.
Microsoft admits it (albeit with an unstatement: "it's not
fully RFC compliant"). The problem is that SChannel indicates
that the maximum SSL packet data size is 5 bytes smaller than
the actual maximum. Thus, any IMAP server which transmits a
maximum sized SSL packet will not work with PC Pine or any
other program which uses SChannel.
It can take a while for the problem to show up. The client has
to do something that causes at least 16K of contiguous data.
Many clients do partial fetching, which tends to reduce the
number of cases where this can happen. However, all software
which uses SChannel to support SSL is affected by this bug.
This problem does not affect UNIX code, since OpenSSL is used
on UNIX.
This problem most recently showed up with the CommunigatePro
IMAP server. They have an update which trims down their maximum
contiguous data to less than 16K, in order to work around the
problem.
This problem has also shown up with the Exchange IMAP server
with UNIX clients (including Pine built with an older version
of c-client) which sends full-sized 16K SSL packets. Modern
c-client works around the problem by trimming down its maximum
outgoing SSL packet size to 8K.
Microsoft has developed a hotfix for this bug. Look up MSKB
article number 300562. Contrary to the article text which
implies that this is a Pine issue, this bug also affect
Microsoft Exchange server with *any* UNIX based client that
transmits full-sized SSL payloads.
_________________________________________________________________
7.44 My qpopper users keep on getting the DON'T DELETE THIS MESSAGE --
FOLDER INTERNAL DATA if they also use Pine or IMAP. How can I fix
this?
This is an incompatibility between qpopper and the c-client
library used by Pine, imapd, and ipop[23]d.
Assuming that you want to continue using qpopper, look into
qpopper's --enable-uw-kludge-flag configuration flag, which is
documented as "check for and hide UW 'Folder Internal Data'
messages".
The other alternative is to switch from qpopper to ipop3d.
_________________________________________________________________
7.45 Help! I installed the servers but I can't connect to them from my
client!
Review the installation instructions carefully. Make sure that
you have not skipped any of the steps. Make sure that you have
made the correct entries in the configuration files; pay
careful attention to the exact spelling of the service names
and the path names. Make sure as well that you have properly
restarted inetd.
If you have a system with Yellow Pages/NIS such as Solaris,
have you updated the service names there as well as in
/etc/services?
If you have a system with TCP wrappers, have you properly
updated the TCP wrapper files (e.g. /etc/hosts.allow and
/etc/hosts.deny) for the servers?
If you have a system which uses xinetd instead of inetd, have
you made sure that you have made the correct corresponding
xinetd changes for those services?
Try telneting to the server port (143 for IMAP, 110 for POP3).
If you get a "refused" error, that probably means that you
don't have the service set up in inetd.conf. If the connection
opens and then closes with no message, the service is set up,
but either the path name of the server binary in inetd.conf is
wrong or your TCP wrappers are configured to deny access.
If you don't know how to make the corresponding changes to
these files, seek the help of a local expert for your system.
_________________________________________________________________
7.46 Why do I get the message Can not authenticate to SMTP server: 421
SMTP connection went away! and why did this happen? There was also
something about SECURITY PROBLEM: insecure server advertised
AUTH=PLAIN
Some versions of qmail, including that running on
mail.smtp.yahoo.com, disconnect the SMTP session if you fail to
authenticate prior to attempting to transmit mail. An attempt
to authenticate was made, but it failed because the server had
already disconnected.
To work around this, you need to specify /user=... in the host
name specification.
The SECURITY PROBLEM came about because the server advertised
the AUTH=PLAIN SASL authentication mechanism outside of a
TLS-encrypted session, in violation of RFC 4616. This message
is just a warning, and in fact occurred after the server had
disconnected.
_________________________________________________________________
7.47 Why do I get the message SMTP Authentication cancelled and why
did this happen? There was also something about SECURITY PROBLEM:
insecure server advertised AUTH=PLAIN
This is a bug in the SMTP server.
Some versions of qmail, including that running on
mail.smtp.yahoo.com, have a bug in their implementation of SASL
in their SMTP server, which renders it non-compliant with the
standard.
If the client does not provide an initial response in the
command line for an authentication mechanism whose profile does
not have an initial challenge, qmail issues a bogus response:
334 ok, go on
The problem is the "ok, go on". This violates RFC 4954's
requirement that the text part in a 334 response be a BASE64
encoded string; in other words, it is a protocol syntax error.
In the case of AUTH=PLAIN, RFC 4422 (page 7) requires that the
encoded string have no data. In other words, the appropropiate
standards-compliant server response is "334" followed by a
SPACE and a CRLF.
The SECURITY PROBLEM came about because the server advertised
the AUTH=PLAIN SASL authentication mechanism outside of a
TLS-encrypted session, in violation of RFC 4616. This message
is just a warning, and is not related the "Authentication
cancelled" problem.
_________________________________________________________________
7.48 Why do I get the message Invalid base64 string when I try to
authenticate to a Cyrus server?
This slightly misleading message is the way that a Cyrus server
indicates that an authentication exchange was cancelled. It is
not indicative of a bug or protocol violation.
The most common reason that this happens is if the Cyrus server
offers Kerberos authentication, c-client is built with Kerberos
support, but your client system is not within the Kerberos
realm. In this case, the client code will try to authenticate
via Kerberos, fail to get the Kerberos credentials, cancel the
authentication attempt, and try the next available
authentication technology.
_________________________________________________________________
8. Where to Go For Additional Information
_________________________________________________________________
8.1 Where can I go to ask questions?
8.2 I have some ideas for enhancements to IMAP. Where should I go?
If you have questions about the IMAP protocol, or want to
participate in discussions of future directions of the IMAP
protocol, the appropriate mailing list is
imap-protocol@u.washington.edu. You can subscribe to this
list via imap-protocol-request@u.washington.edu
If you have questions about this software, you can send me
email directly or use the imap-uw@u.washington.edu mailing
list. You can subscribe to this list via
imap-uw-request@u.washington.edu
If you have general questions about the use of IMAP software
(not specific to the UW IMAP toolkit) use the
imap-use@u.washington.edu mailing list. You can subscribe to
this list via imap-use-request@u.washington.edu
You must be a subscriber to post to these lists. As an
alternative, you can use the comp.mail.imap newsgroup.
_________________________________________________________________
8.3 Where can I read more about IMAP and other email protocols?
We recommend Internet Email Protocols: A Developer's Guide, by
Kevin Johnson, published by Addison Wesley, ISBN 0-201-43288-9.
_________________________________________________________________
8.4 Where can I find out more about setting up and administering an
IMAP server?
We recommend Managing IMAP, by Dianna Mullet & Kevin Mullet,
published by O'Reilly, ISBN 0-596-00012-X.
This book also has an excellent comparison of the UW and Cyrus
IMAP servers.
Last Updated: 15 November 2007
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