AT&T has several ways to relay messages for transmission as text/sms messages to a cellphone:
- <10 digit number>@txt.att.net
- <10 digit number>@mms.att.net
- <10 digit number>@text.att.net
Unfortunately, their email relays seem to be having a LOT of trouble lately.
We're careful to send email to those relays in a measured fashion, with delays between each message, to try to prevent any rate-limiting issues. But still, AT&T seems to periodically just start giving us errors when we try to relay email for those domains.
These errors may last for minutes, hours or days, and then go away for minutes, hours, days, weeks or months. We can find no rhyme or reason to them. It's something going wrong on their end.
The errors look like this:
(host mx.txt.att.net[126.96.36.199] said: 452 4.1.0 <email@example.com> requested action aborted: try again later (in reply to MAIL FROM command))
We've been reaching out to every contact at AT&T that we can find to report the issue and to find a resolution, but as of yet, we have no definitive answer from them as to what is causing the issue, or what can be done to stop it.
We will update here as we learn more.
UPDATE - 2013-09-23 - 21:32 PDT.
While we haven't received any formal information from AT&T, all of a sudden, all queued messages for txt.att.net, text.att.net, and mms.att.net, for some reason, we're able to start relaying email to their servers. We have the rate restricted - no more than a few messages a minute, but it looks like all queued messages are going out, and will continue to go out over the next several hours.
We apologize for the annoyance of the delay in the text messages, as well as how they are all of a sudden starting to flow at night - my cell phone has been buzzing with pent-up messages.
We will keep trying to get real information out of AT&T.