antivirus in smtp, good or bad?

["Stephen J. Wilcox" <steve () telecomplete co uk>]

Hi,
 When investigating our mail queue it seems we have quite a lot of mails which 
are stuck in transit...

Whats happening is we're accepting the mail as the primary MX for the domain but
the user has setup a forwarding to another account at another ISP, they have
antivirus service on that other account. So we get the mail, spool it and try to
forward it but then we get a "550 Error: Suspected W32/MyDoom@MM virus" after
DATA and our server freezes the mail.

Surely this is an incorrect way to do this as there will be lots of similar MXs 
like ours backing this mail up? They should accept the mail and then bounce it?

Thoughts?

Steve