cyrus master fails with status 71

[Eric Cunningham]

Hi list, we're running cyrus imap 2.5.9 built from the FreeBSD 10-2 
(release-p7) ports tree.

The cyrus master process is failing periodically (every 1-2 weeks) as 
follows:

Oct 22 07:38:48 imap1 master[7767]: process type:SERVICE name:imaps 
path:/usr/local/cyrus/bin/imapd age:305.215s pid:32760 exited, status 71
Oct 22 07:38:48 imap1 master[7767]: service imaps/ipv4 pid 32760 in 
READY state: terminated abnormally
Oct 22 07:38:48 imap1 master[7767]: too many failures for service 
imaps/ipv4, disabling until next SIGHUP

This prevents new connections by clients until cyrus is restarted.  I've 
looked around the web but have not seen this issue reported.

A little background:

Our initial thought on this was that we were running out of listen 
queues so have upped that incrementally from the default of 32 to a 
current setting of 32768 via /usr/local/etc/rc.d/imapd using the -l 
option, with increased kern.ipc.soacceptqueue set to 32768, but that 
hasn't helped.  Sometimes the "status 71" occurs during periods of light 
use during off hours, like on Saturday mornings.

We have ~1400 imap accounts, though the number of impad processes hovers 
around 3,000-4,000.  There have been spikes observed as high as 12,000 
imapd processes.  In that particular case, 1 user had 2 imap clients 
accounting for near 6,000 of those connections.  We've attempted to 
limit these high numbers using the following imapd.conf values:

maxlogins_per_host: 50
maxlogins_per_user: 30
tcp_keepalive: 1
tcp_keepalive_cnt: 1
tcp_keepalive_idle: 30
tcp_keepalive_intvl: 900

However, it seems that once these were reached, no new connections were 
permitted and resulted in all manner of user complaints about not being 
able to get at their email.

Any ideas on this "status 71" issue?  Could an upgrade to 2.5.10 
possibly address this?  Thanks!

-Eric