I belong to a number of forums. When I started Anti Spam it sent all the people that had posted on the forum a request for a pass code. With the ability to look for a word or phrase in the Subject field I could have authorized all the people on the forum without having each one send me a pass code. Add a database with key words that would be recognized in the subject line.
A couple examples of key words in the subject are [AmiBroker], [Growwine] and [holygrailism].