Well if you want my honest opinion (and even if you don't) I think its a bad idea because:

1. You will waste server CPU
2. You will waste your bandwidth

Because:

Every spambot on the interweb that finds that address on your page or simply guesses that extrememly common domain prefix will be getting a copy each time they bombard you with a piece of junkmail.

Forms are really to only sensible way these days to get preliminary contacts or leads from your web site IMHO, and once they are internal that is when email once again becomes a useful communication tool.

But yes, if you must the way to do that would be to setup a mail filter to pipe all inbound email to a scripts, then do what you want with it from there.