First of all, let me say that I'm really impressed with Dovecot. It is great.

Problem description

Now I've got a possible bug I'd like to report. I've been learning about the IMAP protocol recently, and have started playing with the IDLE command. The problem is that Dovecot doesn't always notify the client when there is new mail available. While notifications work for the most part, it seems that Dovecot occasionally gets itself into a rut where it fails to notice any changes to the mailbox (new messages, flag changes, etc.). The problem usually becomes apparent when there is more than one email client accessing the same mailbox. In fact, this may be a requirement -- I only tested it once, but I couldn't reproduce the problem when I had only one connection open to the mailbox (which is in maildir format in my case).

An example is included below. Any feedback on how to debug this problem further would be appreciated.

An aside

After I found out about the IDLE command, I looked for implementations. I ran across this plug-in for Apple Mail (one of my favorite mail clients):

http://www.rothwell.us/imapidle/index.html

The web page notes that Leopard's Apple Mail may support the IDLE command natively, which is good news if true. It would be really cool if Dovecot's IDLE command can be made robust enough to make this feature really come alive.

Example

This transcript is copied from an SSL connection directly to dovecot using openssl s_client. At the same time a separate client (Horde/IMP) has the same mailbox open:

A0017 IDLE

• idling

• 7927 FETCH (FLAGS (\Seen \Recent))
• 7927 FETCH (FLAGS (\Deleted \Seen \Recent))
• OK Still here
• OK Still here
• OK Still here
• OK Still here
• 7940 EXISTS
• 22 RECENT
• OK Still here
• OK Still here
• OK Still here
• OK Still here
• OK Still here
• OK Still here
• OK Still here
• OK Still here
• OK Still here
• OK Still here
• 7941 EXISTS

[At some point after this, something happens (or doesn't happen) and dovecot no longer notifies of new messages. The other client is still reading messages in the same mailbox and new mail is still arriving.]

• OK Still here
• OK Still here
• OK Still here
• OK Still here
• OK Still here

[The above message repeated another 30 times here. Finally, IDLE mode is terminated:]

• OK Still here DONE
• 7941 EXPUNGE A0017 OK Idle completed.

[Now a NOOP is issued to gather any more untagged responses, and there's a deluge of responses, presumably all the stuff that happened while dovecot was asleep. Notice that the highest message is 7967 whereas the last one heard about was 7941.]

A0018 NOOP

• 7913 FETCH (FLAGS (\Deleted \Recent))
• 7914 FETCH (FLAGS (\Deleted))
• 7915 FETCH (FLAGS (\Deleted))
• 7916 FETCH (FLAGS (\Deleted))
• 7917 FETCH (FLAGS (\Deleted))
• 7918 FETCH (FLAGS (\Deleted))
• 7919 FETCH (FLAGS (\Deleted \Recent))
• 7920 FETCH (FLAGS (\Deleted \Recent))
• 7921 FETCH (FLAGS (\Deleted \Recent))
• 7922 FETCH (FLAGS (\Deleted \Seen))
• 7923 FETCH (FLAGS (\Deleted \Seen))
• 7925 FETCH (FLAGS (\Deleted \Seen))
• 7928 FETCH (FLAGS (\Deleted \Recent))
• 7967 EXISTS
• 30 RECENT A0018 OK NOOP completed.

Configuration

Here are the specifications of the dovecot used in the above test:

version dovecot 1.0.1 os linux distro centos 4.5 fs ext3 arch x86_64 kernel 2.6.9-55.ELsmp configure --without inotify --with pam_stack --with forcequota2 cc gcc (GCC) 3.4.6 20060404 (Red Hat 3.4.6-8)

In addition, I'm using the deliver LDA as the Postfix mailbox_command, and am using the dovecot-sieve plugin (which is used to set customized IMAP keywords).

dovecot -n:

# 1.0.1: /etc/dovecot.conf ssl_cert_file: /usr/lib/courier-imap/share/imapd.pem ssl_key_file: /usr/lib/courier-imap/share/imapd.pem login_dir: /var/run/dovecot/login login_executable(default): /usr/libexec/dovecot/imap-login login_executable(imap): /usr/libexec/dovecot/imap-login login_executable(pop3): /usr/libexec/dovecot/pop3-login first_valid_uid: 100 mail_location: maildir:~/Maildir maildir_copy_with_hardlinks: yes mail_executable(default): /usr/libexec/dovecot/imap mail_executable(imap): /usr/libexec/dovecot/imap mail_executable(pop3): /usr/libexec/dovecot/pop3 mail_plugin_dir(default): /usr/lib64/dovecot/imap mail_plugin_dir(imap): /usr/lib64/dovecot/imap mail_plugin_dir(pop3): /usr/lib64/dovecot/pop3 namespace: type: private separator: / inbox: yes auth default: default_realm: lava.net verbose: yes passdb: driver: sql args: /etc/dovecot-sql.conf userdb: driver: sql args: /etc/dovecot-sql.conf

ps. Good thing there's no POP IDLE command!