I was just thinking of a way to temporarily disable all login/download access to an account for a particular user, but still allow incoming mail.
This would be great for a billed email service so the user loses no mails but can't check it - by webmail, IMAP, POP, or anything - while the account is "frozen".
You might call the state "frozen", as opposed to there just being an "enabled" or "disabled" state.
Just my two cents. I think it would be a great feature that would be really easy to implement. It would give AMS superior administrative control. This might also be good for "relay only" accounts that are used as form mailers for websites and web apps, etc.