Centos 5 32bit and Zimbra 5.0.10
Major amount of users connected via imap. Everything was fine until the amount of users grown up. Right now Thunderbird has connection problems (timeout), free gives result:
total used free shared buffers cached
Mem: 3368328 3233316 135012 0 150348 1115612
When imap users have connection problem http users works without problem. When I do zmcontrol stop zmcontrol start it's about 600 mb of free memory which then decreases to 100 mb during imap users activity.
Seems the narrow place is imap service.
BTW ms exchange with such amount of users on a similar hardware works without problems.