What's the possibility of have spamfilter forward an incoming message to two different mail servers at or nearly at the same time?  Could it create a copy of the incoming message before sending it and send the copy to one server and the original to another server?  I'd like to have two mail servers with the exact same mail on each so that if one goes down, the other can be accessed.

You need to set up a mirrored server.

Vader wrote: I'd like to have two mail servers with the exact same mail on each so that if one goes down, the other can be accessed.

The way you describe would not have users sent & deleted items.