POPmonitor (OS X) for Mac

From Vechtwijk Automatisering:

Wouldn't it be great if you could delete unwanted e-mail or spam before it reaches your e-mail application? Or delete messages with large attachments without downloading them to your computer first? Or get rid of messages with viruses attached to them? Well, POPmonitor lets you do just that! You can also automate the removal of unwanted messages by creating lists of trusted and blocked senders and by creating custom filters based on several criteria. Another option is to bounce spam right back to the sender to simulate a non-existing e-mail address.

Version 2.1.3 improved existing filters and added new powerful filters; improved ISO character set decoding to properly deal with encoded characters such as � and fixed some bugs.