I'm having an issue with an Exchange 2003 server where the Queue is slowly filling up with emails it can't send (remote servers come back non-responding). The emails are all over the board and I can't find a common thing. For a while the big email target was fbi.gov, not it seems to be Western Union. I have scanned for viruses and malware on all the PCs of the clients computers, but come up with nothing. They have a WatchGuard X55e firewall, so logging is sparse. I assume I have some sort-of botnet on the network somewhere, but I am having trouble tracking it down. Exchange is running on an SBS2003 server.