[Dovecot] performance with 100k messages per folder

Florin Andrei florin at andrei.myip.org
Fri Aug 26 22:07:15 EEST 2011

dovecot-2.0-0.10.beta6.20100630.el6.x86_64 on CentOS 6. Virtual machine 
with 1 GB of RAM on VMWare.

The configuration is more or less stock. Postfix receives then delivers 
to Dovecot. IMAP with mbox. Only one user account, but shared by several 
people via webmail (Roundcube webmail in Apache on the same machine). No 
other MUAs. 100k new messages per month, inbox is rotated monthly into a 
YYYYMM folder by a cron job. Only one monthly folder so far. Messages 
are never deleted (but I may start deleting old folders a year or two 
from now). This is mostly for reading, with occasional messages being 

The email was pretty sluggish when logging in to the webmail interface. 
I asked the admin to increase the RAM from 0.5 to 1 GB. I changed 
mbox_very_dirty_syncs to yes. These measures seemed to accelerate it a lot.

There's still a 1 sec pause when logging in, during which time the 
dovecot/imap process is using a lot of CPU.

It looks like, as long as I give it enough RAM to keep the folders in 
memory, the whole thing should be fast enough, which is great. Any other 
tips-n-tricks to keep the email server speedy and the users happy?

Should I worry about mbox_very_dirty_syncs as long as there are no other 

Florin Andrei

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