Most of the time, these insults are simply ignored, thrown out with all the rest of the mail, I presume. (At least, there are no secret service agents knocking on my door, yet :-)
But one time, I did get a reply.
Someone who knew how to telnet to port 25 had sent me email, in Bill Gates' name, asking to be subscribed to the Insults Mailing List.
My ignorant mail-handling bot promptly signed Bill up for 1 insult a day.
About a week passed, and then I recieved mail from email@example.com. They were the poor soul who had to read Bill's email, they said, and the insults had been a novelty at first, but were beginning to be a waste of their time.
So, I pulled Bill off the list and never heard about it again. I don't know who the guy who reads Bill's mail is or if he told Bill about it, but it's been Kite's closest brush with a Famous Zillionaire yet..