Legitimate email from our MX to @attglobal.net addresses is being blocked.

Their MX rejects the mail with this error message (IP address redacted):

550 unauthorized interface for x.x.x.x on kcin04

We have correct MX and PTR records and no current blacklists hits. The only explanation of what this error message might mean I found on the generic AT&T error message page, which says that the error indicates that

The sending system is not recognized as a valid source of e-mail.


Correspondents should use registered mail systems provided by a major ISP or hosting service.

This server has been in operation for years, and outgoing mail is accepted by the likes of Gmail, Yahoo, Hotmail, etc. How could it not be a "valid source of e-mail"? And what's a "registered mail system" anyway? And does all of this even apply to attglobal.net, or does the generic AT&T page only apply to their other subsidiaries? In which case, how do I find out why we're being blocked?

I did try submitting the block removal request form, but the response I got back was:

We do not show that the IP address(es) listed in your request are on AT&T’s block list

Also, email to @att.net and @bellsouth.net addresses appear to be transmitted without problems, so only attglobal.net seems to be blocking.

  • Nothing but problems with attglobal.net over the last week or so. even the credit card help line number they publish for the U.S. is disconnected and the other business help line had me on musak for 40 minutes with no pick up. I am going to stop by their office tomorrow and ask for a refund. no email traffic for the last 4 hours and not one to call to fix it! – user174725 May 22 '13 at 1:29

I've had problems with AT&T before, and not just with mail. They have a very, er, "idiosyncratic" approach to networks and servers...

They're probably using some white-listing system which only includes known ISPs and e-mail services, such as Spamhaus's whitelist. There's no way to tell, or if so which whitelist(s) they're using, but it's probably not a bad idea anyway to get your server listed on any whitelists you can find. (Google "e-mail server whitelist", etc. There are a few of them.) But it's still possible AT&T operates their own whitelist. *headdesk*...

In the meantime, you should still always be able to send mail to postmaster@domain.tld (and if not they're in violation of RFC2821 section 4.5.1) and ask the mail server admins why you're being blocked or what to do to get unblocked.

  • My previous attempts to contact postmaster@attglobal.net were unproductive. I plan to try again next week though. – depquid May 18 '13 at 11:52
  • I'm curious if you've heard back from the attglobal postmasters? – Isaac Freeman May 25 '13 at 17:40
  • Not yet. I'm still trying... – depquid Jun 3 '13 at 14:03
  • Try rm-hostmaster@ems.att.com listed in their who is info. – Isaac Freeman Jun 5 '13 at 2:38
  • Yeah, no response. Also, postmaster@attglobal.net is now bouncing, even when I send to it using a Yahoo email address. The 800 number is reconnected, but their tech support told me they'll only talk to their own customers. – depquid Jul 2 '13 at 12:41

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