If I can ignore subscribe and unsubscribe, this would mean, I can always return an OK as Server Response, without care about what kind of LSUB command came in, right? I would handle every mailbox as subscribed. I should only look if the asked mailbox exist?
An IMAP client can ignore LSUB/SUBSCRIBE/UNSUBSCRIBE and still work well. (In fact, the client I'm using this very moment does.)
An IMAP server must implement LSUB and friends.
Arnt
