We have physical Zimbra servers, but we are trying to virtualize our application servers. Our app servers host our Web site, which we integrate with Zimbra via the preauth mechanism. Unfortunately, in our tests we're seeing intermittent problems with preauth failing for users on our virtual app servers. We see statements like this in our mailbox.log files on our Zimbra servers (some info redacted):

authentication failed for user-AT-domain.com, preauth timestamp is too old, server time: Mon Sep 27 14:20:49 PDT 2010, preauth timestamp: Mon Sep 27 14:26:01 PDT 2010

There are basic issues with keeping the system clock running the same on virtual servers as on physical servers, so I suspect we might have similar problems if we had physical app servers and virtual Zimbra servers. Is there some way to relax the 5 minute time window for the preauth token? Or is there some other way to do preauth with Zimbra that won't break if the system clocks on the various systems drift out of sync?