If you have one extension number and several mailbox users then use the COS attribute #32:
"STATION HAS MULTIPLE MAILBOXES, ASK BEFORE CONNECTING.".
If you have several extensions and one mailbox, it can be difficult to divert to the Serenande.
Put the 3 extensions into a group and make group overflow/diversion to the Serenade. make a group mailbox in the Serenade.
The users can log in to the group mailbox in the Serenade and liten to their messages.
///doktor