I've been using maildrop for quite a while now and I need to expand my capabilities. Specifically, I use maildrop with spamassassin to catch almost all incoming spam. It's the ones that get through that I want to create some additional filters for. Apart from the maildropfilter man page, are there any good howto's for creating pattern matching filters? Specifically, I'm looking for something with real examples that make user of tricky syntax.