FYI, seems to be a bug to this behavior.. support team said the fix should be out Q1 2008..
http://bugzilla.zimbra.com/show_bug.cgi?id=11267
In the mean time, zmclamd restart should fix the issue.. but i can't imagine if clam fails 4 AM in the morning.. all mails got stuck along the way.. Surely will get me spanked by my boss by the time i arrive at office the following morning
