Hard to understand your scenario. Are calls flowing through Lync to the associated UM AA for the UM Dial plan associated with Lync? Then is the caller trying to use speech or using directory lookup or simply entering in a number? From what
I can tell from the information you gave the UM AA is attempting to transfer out to a destination. Can I assume this is a Lync EV user? If so, is the Lync user UM enabled with both the SIP and "extension" EUM addresses? Try to increase the
logging level for UM and see the integration data for the failed call where you are expecting it to integrate to a mailbox and see what integration is passed to UM.