You make fine points. But mail-filtering, while a good example, is not exactly something that an average user knows how to do.

My point is, that I try to keep the application expressive but not intimidate newbies with bunch of options that are hard to understand.

That said, your proposal in my estimation would be very easy to implement. So I may make it in the future. Putting it away into some sub-page like "Advanced" or something. I'll at least write your suggestion down, but can't promise when I'd do it. Too much work already, too little time.