Members of the 'Unaddressed Messages' distribution list created by Unity setup are send all undeliverable messages from outside callers (i.e. they were sent to a mailbox that was full or the like).
Make sure your account is included in the membership list for this distribution list.
Remember, however, if subscribers send the message, they receive the NDR in that case (i.e. the unaddressed messaged dL is only used when the sender is unknown).