I own several domains and have to say please don't bounce spam back to the sender, almost all the time the From/ReplyTo fields are spoofed using legit domains with invalid user names (I've seen them even use real user names to make it worse).
So between my postmaster accounts and users complaining that they never sent the email bouncing spam to the given address is a bad practice. I can forward you all my bounce backs for 24 hours if you'd like to see
I'm usually not narrow minded but I don't see a use for this feature that 'reply' can't do (maybe for mass replies...there's a thought, if you don't want to go the mailing list route)