Dovecot running within a FreeBSD Jail can create some interesting issues. One issue that affected my mail server today was time moving backwards (37 seconds, according to Dovecot as reported in the /var/log/maillog):
May 4 21:45:17 mailhost dovecot: Fatal: Time just moved backwards by 37 seconds. This might cause a lot of problems, so I'll just kill myself now. http://wiki.dovecot.org/TimeMovedBackwards
This happened after a reboot of the host system. I went to check the mail, using a Mail client, and I could not connect to the mail server. Upon examining /var/log/maillog, the above line got me to thinking that I had let the jail attempt to change the system clock. So the first step to tracking the problem down is to comment out the adjkerntz line in the /etc/crontab file:
# Adjust the time zone if the CMOS clock keeps local time, as opposed to # UTC time. See adjkerntz(8) for details. #1,31 0-5 * * * root adjkerntz -a
Although this may not be the only thing necessary to fix the problem, I know from a quick search of “jail + adjkerntz” that it is customary to comment out this line as a matter of setting up the jail properly.
The error code references a hint into the nature of the problem: http://wiki.dovecot.org/TimeMovedBackwards
The quick way to work around the problem (should the above not work next time I restart) is to restart the jail once the host system has stabilized:
/etc/rc.d/jail restart jailname
As I dig out more details, I will post them as edits to this post.