MailMender 1.1 - Spam Filter

MailMender combines keyword filters with challenging senders of suspicious mail to keep junk email out. The authorization process is simple yet inflexible, though, MailMender only supports POP accounts, and it could be easier to operate. MailMender is no longer available.

Challenge/response mail filters are a simple idea that works well to keep spam out. Only mail from known senders is allowed through while new sources are sent a challenge that allows them to proof their being legit senders. Unfortunately, such filters generate a lot of unnecessary traffic to spammers (or their nonexistent addresses, rather) while senders of legitimate newsletters can have a hard time authorizing with their subscribers.

To tackle the first point, MailMender, a simple implementation of a challenge/response filter, also includes relatively smart keyword filters and looks for other characteristics to identify possible spam. By default, only unknown senders of such messages are challenged to authorize by replying with a (customizable, but not unique per sender) keyword in the subject.

Unfortunately, MailMender does not release the original message once the sender has responded to the challenge. To get the message through, it has to be re-sent with the correct keyword. Of course, you can also review "killed" mail and restore it manually or authorize senders by hand.

While it's nice that MailMender allows you to send complaints easily (they could be better and more precise, though), it is a pity that it only supports POP accounts. This it does in a straight-forward way, though, simply removing all mail it objects with.