I know I'm really late to this party, but a situation has come up where keeping a mailbox, deleting all incoming mail and forwarding onto another box is a needed situation.
I have a client who has an employee who is going out on maternity.
They want to both preserve her existing mail, but forward all newly incoming mail to another user.
I would think that keeping a mailbox intact would be ideal so they can pick up their mail when they return from leave would be wise, but without getting any new incoming mail - which is now being forwarded to another user.
At any rate, I'm going to disable the mailbox after forwarding some of the mail to the other user, and just enable the forward, because I don't want any shenanigans...
Anyhow, more an a response to Stephen's question about why you would want this set up. Maybe there's a better way to do it, and I'm all ears!