HI,
I am using zimbra GA 6.0 64 bit server. Since lat two days i am facing the problem of the clamd. clamd not started using zmcontrol start. It show the error of main.cvd not available.
In clamd.log file it's show
Can't open file /opt/zimbra/data/clamav/db/main.cvd

I also try this link
ClamAV - Reset Defs DB - Zimbra :: Wiki
But still it fail.
When anti virus service fail my mta also gone fail at the same time.