Use one of the classic BOFH methods:
- write a procmail recipe that deletes enough mail from his inbox to
make space for the new message.
- delete his mail account.
- use your clue-stick[*] to teach the user to read his mail.
You can't do much else: if the box is full there's nothing you can do
with the message except reject it. Making the mailbox bigger isn't a
solution, merely a delaying tactic.
[*] where clue-stick = electric cattle prod. Every BOFH has one.
--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |