These aren't the best forums for adding rulesets to SA. SA has it's own email users list and there are lots of general forums writing about it.
Or you can use the exim system filter, but you'll need to learn how to use it by reading exim.conf, and then you'll be responsible for keeping track of changes to it yourself as it getsupdated.
Or you can of course modify exim.conf file but then you're on your own.
Jeff