If you have an idea about how to improve POPFile, you can submit it as a Feature Request (You have to login to the server to request a feature. Please choose 'enhancement' in the Type section).
Before you do this, however, it is a good idea to read through the other registered Feature Requests and to discuss your suggestion with other users and devlopers on the Discussion Forum. Sometimes a discussion is far more likely to get the developers excited about a new idea.
One popular request we are working on is suppressing spam delivery so your mail client will never see the spam. There are also certain things that are not going to be added to POPFile even though frequently requested. The top on that list would be to bounce messages back to spammers. See our FAQ page on bouncing.