Watermark test working too good

[Daniel Straka]

I've got some users that subscribe to a state library newsletter sent out via distribution list. These messages arrive with a null sender and MailScanner' watermarking feature is marking them as spam (yes, I have it set to do that). 
Question is, if I add the relaying servers IP address to my spam.whitelist.rules file will the messages bypass MailScanners watermark test?

Is there another way to have these messages bypass the watermark test?

Thanks,
-- 

Dan Straka
Systems Coordinator
Casper College
307.268.2399
http://www.caspercollege.edu