I recently had enough of all the "*** GMX Antispam ***" lines in my kmail junk folder and tried to get rid off it. (It also marked false positivies in my incoming folder which also annoyed me).
Here's a small guide to strip the "*** GMX Antispam ***" string from your mail's subject (notice: this won't sort your mails in your junk folder, it only strips the subject line):
