I am currently running Zimbra OSE version 4.0.3 on a CentOS 4 (RHEL 4) server. I am running in a split domain mode, as I am evaluating Zimbra as a possible replacement for our current POP3-only Linux-based email server. Right now I only have two active accounts on the Zimbra server; my own and a 'spam dump' account, which gets email tagged as spam by our email gateway server. The last couple of days I have been running into an issue where email messages are getting stuck in the Active mail queue. Today the queue got up to over 800 messages, which had been accumulating for over an hour, before I finally stopped and restarted Zimbra and cleared out a bunch of messages to the 'spam' account, as I don't really care about these. Looking around the system for clues on what is causing this problem, I came across errors like the follow in the /var/log/messages file:

Nov 7 14:23:59 email amavis[1803]: (01803-04-7) (!!) TROUBLE in check_mail: spam_scan FAILED: timed out
Nov 7 14:23:59 email amavis[1803]: (01803-04-7) (!) PRESERVING EVIDENCE in /opt/zimbra/amavisd/tmp/amavis-20061107T114500-01803

The time on the first message I see like this pretty much coincides with the time I start noticing things stuck in the queue. Once the first error is logged I see the same type of error messages repeating in the log. I don't really know if this error is indicative of the cause of the problem, or perhaps they are a result of some other issue. I'm not seeing any other error messages, although maybe I just don't know where to look.

I know the 'spam' account is receiving a very high volume of email messages, and this may be part of the problem. However, I am concerned about why the large volume would cause this backup of messages. If we decide to go live with Zimbra we will have between 300-400 active accounts, and this type of issue would not be good.

Any help on solving this problem would be greatly appeciated.