Linux Mail Server Setup and Howto Guide

Hello Consultant!

It´s me again! :D

I followed this article to set up my mail server: http://www.linuxmail.info/post…..-centos-5/. I also configured secure IMAP, POP3 and SMTP (on another server) with SSL.

Overall, everything works fine. I´ve got about 8k users which most of them use POP3 but there is a large portion of users that user IMAP and Webmail.

Users are able to send and receive email authenticating agaisnt a Win2k3 Active Directory + secured connections with SSL.

Besides some other problems (that I posted in this forum), there is a problem that dovecot hangs at times. It may be a coincidence, but it happens everyday at about 9:00/9:30am, 11:20am, 1:50pm and 2:30pm (as far as I have monitored/been told), which are the hours that users come to work and return from lunch break.

When dovecot hangs, i restart its service and all is good again. I used to think that my AD was being overwelmed with authentication (regular windows login and dovecot), but I installed a new AD server on Win2k3 Enterprise Edition 64bits on a new and powerfull hardware and the problem persists.

My mail server is installed on an identical hardware with RHEL 5.4 64bits. Dovecot 1.0.7, Postfix 2.3.3.

Thanks a lot in advance!!

Mario Gomide

Hey Consultant!

Well, I changed the authentication method to Kerberos and it works fine. But dovecot still hangs at times…

I really don't know what else I could do. As a lousy workaround, I made a script that restarts dovecot everyday at 9am and 2pm.

I don't think this is the issue, but I got about 7000 users that I suppose dovecot can handle perfectly even with SSL.

Thanks again!

Mario

Hello again!

Well, I didn't have a time syncronization problem, but thanks for the advise.

I changed my structure to a new server, and so far so good. Still no problems with dovecot hanging.

I made some interesting chages:

Dovecot now uses passdb pam instead of passdb ldap;

System doesn't use samba, nor winbind nor changes in nsswitch;

Dovecot no longer hangs (considering that this is end-of-the-year period, and people here usually don't check their emails and stuff, lots of people in vacation, so the load is a lot lower).

Thanks!

Mario

Ok, after some research, it seems that the problem is related to the maximum number of open file descriptors.

I noticed I have tons of these mesagens in maillog:

I got about 8000 users, connecting via SSL (POP3 and IMAP) + webmail connections.

But the question is: Should I do anything with dovecot? Is it only increasing 'ulimit -n'? Any other recommendactions?

Thanks!

Hey,

My login_process_size is already set to 64, but login_max_processes_count was at 128.

Then I issued the following command every second:

ps -ef | grep imap-login | grep dovecot | wc -l

The results were in between 149 and 152.

and my webmail already was starting to get slow at this time (2:24pm) and dovecot is about to hang.

I changed login_max_processes_count to 256 and restarted dovecot. Ten minutes after, my processes are increasing slowly. All is fine (as usual after I restart dovecot).

Hope this fixes the problem. The next "hanging" would be on monday at about 9:40am.

Great news, folks!

So far, the mail server is working fine, with no problems at all.

I think the problem is solved!!!!

If I have trouble or if something went bad, I'll let you know!

Thanks a lot again!

Mario