I run Zimbra on a virtual machine. It's not ideal to run it like this; it does like to have a fair bit of CPU time available.
Sometimes it fails - usually when the VM gets shutdown unexpectedly. Most recently I discovered I wasn't getting email due to clamav not working - this was sometime after upgrading from 4.5 to 5.0, although 5.0 had been working.. The Zimbra watchdog was attempting to start it every few minutes and the host machine's CPU time was disappearing rapidly.
I spent some time looking at the configurations, wasting time wondering why the zimbra/clamav/etc/ files were defaults (it doesn't matter, they're not used).
Eventually I deciphered the log message: ERROR: MD5 verification error
It means, delete the contents of zimbra/clamav/db/, then run 'sudo -u zimbra zimbra/clamav/bin/freshclam'.
This is the first time I've ever seen ClamAV corrupt its database.
I consider myself an expert on installation, deployment and management of Postfix, amavisd-new, ClamAV... but they're well integrated with Zimbra so problems like this can often not be as obvious as they should be.
