Blocking mail from certain email clients

[Alex Chejlyk]

Hello list,

I've been receiving hundreds of non delivered emails. These emails were 
not sent by me, they are spoof emails.

The only consistent thing I see is that the spoofed emails are from 
Outlook express, the domains keep changing so I'm assuming it is a 
Windows virus causing this mayhem.

Is there a way to block email that comes from Outlook express? I'm 
asking before I've done any research because I'm currently up to my 
eyeballs with another project.

Thanks,

A