Re: IMAP stops responding.

[Joseph Tam]

S?ren Peter Skou  writes:


I've experienced that IMAP/IMAPS stops responding.  To restore service
there is only one way, restart Dovecot completely.  This leads to
services being interrupted for some people, so it seems to only affect
some of the users on the server.  But POP3/POP3s is still running
happily.  Also, it happens more as we approach Rush Hour.


Help us help you: the problem is most likely pointed out in the log files.
Also, a dump of your configurations (doveconf -n) would help.

Offhand, it seems you've hit an IMAP resource limit, such as
mail_max_userip_connections, or perhaps process/memory limits
(e.g. process_limit, vsz_limit, etc.).

Joseph Tam 

Re: IMAP stops responding.

[Bill Shirley]

See NATing comment below.

Bill

On 10/20/2017 5:24 AM, Søren Peter Skou wrote:

Hiya all,

I've experienced that IMAP/IMAPS stops responding. To restore service there is 
only one way, restart Dovecot completely. This leads to services being 
interrupted for some people, so it seems to only affect some of the users on 
the server. But POP3/POP3s is still running happily. Also, it happens more as 
we approach Rush Hour. All of this leads me to believe that we're facing a 
problem with clients somehow. I've searched the net for the problem, and dating 
back I've found references to Apple units being the culprit. So we've taken an 
old Apple client, and tried to see how many sessions it actually starts, the 
result of that test was that regardless what we tried it only opened one extra 
session.

A bit of information, Debian OS :
dovecot-core   2:2.2.27-1~auto+44amd64
secure POP3/IMAP server - core files
dovecot-imapd  2:2.2.27-1~auto+44amd64
secure POP3/IMAP server - IMAP daemon
dovecot-mysql  2:2.2.27-1~auto+44amd64
secure POP3/IMAP server - MySQL support
dovecot-pop3d  2:2.2.27-1~auto+44amd64
secure POP3/IMAP server - POP3 daemon
dovecot-sieve  2:2.2.27-1~auto+44amd64
secure POP3/IMAP server - Sieve filters support

the Config itself is fairly simple, lookup through MySQL to find 
username/password etc - I don't really see any obvious option. Also, limiting 
users/sessions per IP isn't really a good idea as we have a great deal of 
customers behind NAT.

NATing shouldn't matter.  The way I understand mail_max_userip_connections, it 
is per user and IP.  Therefore
(the default being mail_max_userip_connections=10), bob, sally, and tom will 
each get 10 connections
from the same IP address.

Med venlig hilsen/Best regards

Søren P. Skou
Netværkstekniker

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Teglholmsgade 1
0900 København C

Tlf: 69 12 12 12
E-mail: s...@danskkabeltv.dk
Web: www.danskkabeltv.dk

IMAP stops responding.

[Søren Peter Skou]

Hiya all,

I've experienced that IMAP/IMAPS stops responding. To restore service there is 
only one way, restart Dovecot completely. This leads to services being 
interrupted for some people, so it seems to only affect some of the users on 
the server. But POP3/POP3s is still running happily. Also, it happens more as 
we approach Rush Hour. All of this leads me to believe that we're facing a 
problem with clients somehow. I've searched the net for the problem, and dating 
back I've found references to Apple units being the culprit. So we've taken an 
old Apple client, and tried to see how many sessions it actually starts, the 
result of that test was that regardless what we tried it only opened one extra 
session.

A bit of information, Debian OS :
dovecot-core   2:2.2.27-1~auto+44amd64
secure POP3/IMAP server - core files
dovecot-imapd  2:2.2.27-1~auto+44amd64
secure POP3/IMAP server - IMAP daemon
dovecot-mysql  2:2.2.27-1~auto+44amd64
secure POP3/IMAP server - MySQL support
dovecot-pop3d  2:2.2.27-1~auto+44amd64
secure POP3/IMAP server - POP3 daemon
dovecot-sieve  2:2.2.27-1~auto+44amd64
secure POP3/IMAP server - Sieve filters support

the Config itself is fairly simple, lookup through MySQL to find 
username/password etc - I don't really see any obvious option. Also, limiting 
users/sessions per IP isn't really a good idea as we have a great deal of 
customers behind NAT.

Med venlig hilsen/Best regards

Søren P. Skou
Netværkstekniker

[logo]


Teglholmsgade 1
0900 København C

Tlf: 69 12 12 12
E-mail: s...@danskkabeltv.dk
Web: www.danskkabeltv.dk