[Dovecot] imap login fails with "no auth attempts"

[Niels Richter]

Hi,

I'm currently facing a strange behaviour of dovecot 1.2.10 (and
before): after some days the login into our mail servers stops working
for imap-connections. pop3-users can go on with using dovecot. Looking
into the logfile I can only find:

[...]
imap-login: Disconnected (no auth attempts)
imap-login: Disconnected: Shutting down (no auth attempts)
[...]

as a hint what is maybe happening. After restarting the system is
working quite well again for some time. There is no extra load and not
other special at the server running. The authentication is handled
over mysql.

This is our dovecot -n output (relevant parts):

# 1.2.10: /usr/local/etc/dovecot.conf
# OS: FreeBSD 7.2-STABLE i386  ufs
protocols: imaps pop3s pop3 imap
ssl_ca_file: /usr/local/etc/ssl/...
ssl_cert_file: /usr/local/etc/ssl/...
ssl_key_file: /usr/local/etc/ssl/...
disable_plaintext_auth: no
login_dir: /var/run/dovecot/login
login_executable(default): /usr/local/libexec/dovecot/imap-login
login_executable(imap): /usr/local/libexec/dovecot/imap-login
login_executable(pop3): /usr/local/libexec/dovecot/pop3-login
mail_max_userip_connections(default): 20
mail_max_userip_connections(imap): 20
mail_max_userip_connections(pop3): 10
verbose_proctitle: yes
first_valid_gid: 0
mail_access_groups: mail
mail_privileged_group: mail
mail_location: maildir:/usr/...
mail_executable(default): /usr/local/libexec/dovecot/imap
mail_executable(imap): /usr/local/libexec/dovecot/imap
mail_executable(pop3): /usr/local/libexec/dovecot/pop3
mail_process_size: 512
mail_plugin_dir(default): /usr/local/lib/dovecot/imap
mail_plugin_dir(imap): /usr/local/lib/dovecot/imap
mail_plugin_dir(pop3): /usr/local/lib/dovecot/pop3
imap_client_workarounds(default): delay-newmail outlook-idle
netscape-eoh tb-extra-mailbox-sep
imap_client_workarounds(imap): delay-newmail outlook-idle netscape-eoh
tb-extra-mailbox-sep
imap_client_workarounds(pop3):
namespace:
  type: private
  prefix: INBOX.
  inbox: yes
  list: yes
  subscriptions: yes

Do you see anything which is unclear or unnecessary and could lead to
a crash of the imap-login process after some time?

Thanks for your help!

-- 
Niels.