Here's the deal, I'm moving to Zimbra soon and need to see if it can handle this situation that my current aging (see decrepit, ancient, poo) setup can't deal with.

This cycle happens a few times on some servers. I turned off bounce messages to stop it. The sender is blank with a faked return address.

This is a somewhat common situation I've been seeing over the last couple months, is this easily stopped via Zimbra?
I know the faked returns are not, but how about filtering them via the spam filter or some sort of watermarking?