automated mail server stress testing?

[Chris Yuzik]

Just wondering if there are any programs/scripts/whatever that can put 
an artificial high load on our new server so we can see if anything 
breaks *before* we start moving real users to this new box.

Ideally, I'd like to create a hundred or so (fake) users, then hit this 
box with ridiculous amounts of mail (and artificial spam/viruses too) so 
we can make sure it handles the load without breaking, doesn't let 
viruses through, etc.

Anyone aware of an automated server stress tester such as this?

Thanks,
Chris