Since you've written the program, it shouldn't be too difficult to toss in something to scan the headers and subject line, and shunt mail meeting some criteria on an exclusion list -- which you would work out -- to /dev/null.

I'm not sure of any specific modules/packages out there for this off the top o' me head, but I'm sure there are a few out there, and if not, do what we all do from time to time: write your own. :)

Hope this helped,
-v.