Does anyone have a link to a good reference on the antispam/virus that zimbra uses?

We just migrated to Zimbra (open source edition), and have had reports from users of not receiving legitimate emails. If they are not in their junk folder, does that mean they have been permanantly deleted? or are they quarantined somewhere for a time period? If they are stored somewhere, how can I view the messages (or at least the to/from and subjects) and deliver the messages to the users?

Have spent about a day digging, but having a hard time finding any documentation to help.

Thanks,
Walter.