How can I reject based on X-Mailer:

[Bryan Guest]

Hi:

We could use some assistance...

My company is getting mailbombed by some spammers.  By some bizarre comedy 
of situations Postini does not seem to be able to filter out this spam. 
(Reduced staff due to Martin Luther King day?)

We use MailScanner locally to do local virus scanning but not spamassassin.

Is there a way I could get MailScanner to filter based on the X-Mailer: 
header?

The only common link I see in this spam is the contents of this header. 
Everything else (Sender IP's, To: and From: ) is forged.  The body is text 
(random words) which changes with each message and the actuallspam is a 
graphic attached to the message.  The filename of the graphic changes 
randomly.

So to reiterate, is there anyway anyone knows to filter based on X-Mailer:?

If so please reply or email me at bryan_guest at hotmail.com

Thanks
Bryan