i did some searching in the mailman code and have discovered that mailman uses the VERBOSE flag to the python regular expression package, which means that unescaped spaces in the regular expression are ignored. so you need to change the topics to be like: CentOS\ 4\ i386 or: CentOS[ ]4[ ]i386 i'm not sure how many backslashes will be necessary to make it through to the module correctly, so brackets may be easier. or you could change the subject line format to be more like: CentOS-4-i386 so you could match without spaces.