Yes, there are two ways to do this, first you can use the DID table to send incoming calls for 301 to 321 and as this is applied at this level, the calls are considered by the system as having an initial destination of 321 so calls will end up at the 321 mailbox. Second method I would have to check up on but IIRC there is a way of putting a code in the DID table that effectively sends it to the mailbox you specify there, but I have never used it myself and would have to check the documentation in order to help with that. Maybe Belvedere can help with this method.