dovecot - Apr 2013 - login crashes - maybe too many simultan connections

Hallo,

since a few days, users sometimes have problems connecting to our 
mailserver, in the mail.err are many lines like this:

Apr 23 11:14:25 psy2 dovecot: dovecot: child 17607 (login) killed with signal 11
(core dumps disabled) (ip=xx.xx.146.84)

Users who are already logged in keep connected, but new connections are not
possible.This happens only between 10 am and 3 pm, never in the early morning or
at night, so i assume, maybe this is caused by too many simultaneous
connections?

After restarting dovecot the problem is temporary solved, new users may connect,
but after one or a few days, this may happen again.

# 1.2.15: /etc/dovecot/dovecot.conf
# OS: Linux 2.6.32-5-amd64 x86_64 Debian 6.0.1
log_timestamp: %Y-%m-%d %H:%M:%S
protocols: imap imaps pop3 pop3s
disable_plaintext_auth: no
login_dir: /var/run/dovecot/login
login_executable(default): /usr/lib/dovecot/imap-login
login_executable(imap): /usr/lib/dovecot/imap-login
login_executable(pop3): /usr/lib/dovecot/pop3-login
mail_privileged_group: alle
mail_location: maildir:~/Maildir
fsync_disable: yes
mbox_write_locks: fcntl dotlock
mail_executable(default): /usr/lib/dovecot/imap
mail_executable(imap): /usr/lib/dovecot/imap
mail_executable(pop3): /usr/lib/dovecot/pop3
mail_plugin_dir(default): /usr/lib/dovecot/modules/imap
mail_plugin_dir(imap): /usr/lib/dovecot/modules/imap
mail_plugin_dir(pop3): /usr/lib/dovecot/modules/pop3
auth default:
   passdb:
     driver: pam
     args: dovecot
   userdb:
     driver: passwd

May anybody help? Thanks in advance!

Greetings from Frank.

On 24.4.2013, at 9.13, Frank Leonhardt <leo at psychologie.tu-dresden.de>
wrote:
> Apr 23 11:14:25 psy2 dovecot: dovecot: child 17607 (login) killed with
signal 11 (core dumps disabled) (ip=xx.xx.146.84)
That's a bug.
> # 1.2.15: /etc/dovecot/dovecot.conf
But you're using a way too old version. It's highly likely that it's
already been fixed. Only v2.1 and newer is actively supported right now.