I can't really care less about those people. Most people I'm talking about are people who're contacting me because I already provided them quite a bit of free service via my free software.

So if someone can't be bothered to check so that I'm not wasting time responding to their trash folder, that's a good filter in the first place.

Anyway, better thing might be responding by adding a (F)AQ item publicly, and just sending a link.