I'm running 4.5.6 (network edition, professional) on a dell machine with 6GB ram for about 200 users, I would say a large majority are Outlook users with the ZCO Connector.

Today I had to restart zimbra because people couldn't connect. I checked out the mailbox.log and found:

2007-10-01 11:55:51,929 WARN [http-443-Processor66]
[name=xxxxxx@xxxxxxxxxx.com;mid=221;ip=xx.xxx.xx.xx ;ua=ZimbraConnectorForOutlook/4.5.288;]
dbconn - Connection pool is 75%
utilized. 28 connections out of a maximum of 37 in use. Turn on debug
logging for zimbra.dbconn to see stack traces of connections not returned to
the pool.

.....
Oct 1, 2007 11:53:53 AM org.apache.tomcat.util.threads.ThreadPool logFull
SEVERE: All threads (100) are currently busy, waiting. Increase maxThreads
(100) or check the servlet status

So yes, I read the message and I should increase the maxThreads in my server.xml -- but by how much?

Is it worth installing Lamda Probe (Home - Lambda Probe) to see my thread usage and figure it out from there? Or should I just double maxThreads up to 200?