The Microsoft Exchange Unified Messaging service on the Mailbox server received a diverted call with ID "%3" for extension ...

The Microsoft Exchange Unified Messaging service on the Mailbox server received a diverted call with ID "%3" for extension "%1" on UM dial plan "%2" from UM IP gateway "%4", but no UM-enabled mailbox for the corresponding extension could be found. Please check the extension and make sure that the corresponding mailbox is enabled for UM and associated with the correct UM dial plan.