This is a great features but severely cut off at the legs. Currently, unless I've really missed something, it can only post to one category. This is too restrictive. Why not allow multiple "Post by email" profiles?
Each profile can REQUIRE (not optional like currently) a keyword to be inserted into the subject line. You could use a category alias for instance and that will trigger the related profile which posts to the specified category.
Or did I just miss how to accomplish this already?