In Messaging, faxes fail because of one or more of the missing basic provisioning requirements. To validate if you have implemented fax properly, see Implementing fax.
Condition: You have configured CoS for fax support. However, the fax email is unavailable.
Result: The system rejects the fax at transmission time.
Condition: You have configured CoS for fax support. However, the fax email is unavailable and the AxC is offline.
Result: The system sends the fax to the postmaster account.
Condition: You have configured an incorrect email address.
Result: The system sends the DSN to the postmaster account.