AT&T SMS Server Reply "try again later", Unable to Send Text Message to AT&T Wireless Users, Dec2018

AT&T SMS server is replying with error message to received email.  Without accepting the email, AT&T is not sending text message to Wireless phones. Intermittent issue, but lasting for days.

Error response: "452 4.1.0"  and "try again later" (in reply to MAIL FROM command)

Responding AT&T server: mx3b.txt.att.net[166.216.152.132]

Our organization depends upon AT&T to provide email access to enable sending of text messages to AT&T Wireless system users.  We have safety and security policies which assume cell phone carriers deliver email messages as text messages to the cell phones of our employees.  Each cell phone carrier has an SMS system which includes an internet domain accepting email in the format of @.  The domain for AT&T is "@txt.att.net".  

Since November 27, 2018, for periods lasting hours and days, AT&T SMS system response to our email messages has been "try again later".  Try again later is not acceptable in security and emergency situations.  The system was unavailable afternoon of Nov 30 through morning of Dec 3, and for hours during afternoon to morning of Dec 3-4, mornings of 5, 6, and 7.   I checked one month of logs.

I understand the concept of "too busy to help", but not where SMS is concerned and when trying again after a reasonable time does no good.  None of the other carriers have the problem, and we cannot re-write third party solutions that don't have ability to "try sending the message again, later."

* Is AT&T experiencing denial of service attacks?  Please let us know, and we will adjust according to when you expect a solution.

* Is AT&T doing maintenance on servers?  Please let us know, and we will adjust according to when you expect a solution.

* Does AT&T need to replace the hamsters in their SMS server(s)?  Don't forget to lubricate the bearings on the wheel, and get it done quickly, please.