Thanks - yes, that's just what I was thinking. I've never seen anyone do that and I wonder why. Any kind of input verification, regular expressions or whateve

Thanks - yes, that's just what I was thinking. I've never seen anyone do that and I wonder why. Any kind of input verification, regular expressions or whatever is only going to catch some of the error cases but the goal of the game is to catch as many as possible. The regular expression at the top of this thread is interesting but I don't think I'd use it - instead use a simpler regex to catch most obvious errors (and disallow root@localhost, as someone pointed out) and couple it with an ajax check-the-mail-server thing. I think I'll try this.