The original message was received at Tue, 30 Apr 2019 16:11:17 -0400
from m0053301.ppops.net [127.0.0.1]

----- The following addresses had permanent fatal errors -----
<peering@att.com>
(reason: 550 5.1.1 <peering@att.com>... User unknown)

----- Transcript of session follows -----
... while talking to [144.160.112.16]:
>>> DATA
<<< 550 5.1.1 <peering@att.com>... User unknown
550 5.1.1 <peering@att.com>... User unknown
<<< 503 5.0.0 Need RCP