Advanced filters

[Michael Smith]

Hey all,
    I've trying to develop a decent set of filters for spam and I was 
hoping that I could have a filter search the message body for key terms 
(i.e., "unsubscribe=XXXX"). the current filter rules for moz 1.1+ do not 
seem to have this capability. Any help on how to create a custom header 
or script that would allow me to do this would be greatly appreciated

Thanks
Mike Smith