Ask Al: Help, I'm blocked at AT&T!

Jay writes: Al, I am getting the following message on several email related to AT&T: flph260 DNSBL:ATTRBL 521<>_is_blocked.__For_information_see_ After going the ATT site, using Spamhaus to check the IP as well as using AT&T's submittal removal site, I am at a dead end as to how to get this resolved. Spamhaus came up showing no problem. Any help would be appreciated.

Jay, there are a few different reasons somebody can get blocked at AT&T, from what I can tell.
  1. A significant spike in sending volume or spam complaints.
  2. A significant spike in sending volume or spam complaints in the same network neighborhood as you (meaning other sending IP addresses in a /24 may have caused the blocking).
  3. Some really bad stuff is going on, sending some sort of affiliate spam or really, really unwanted stuff that they're able to identify and/or fingerprint through various means that they don't disclose.
Maybe there are other reasons or circumstances under which AT&T will block mail from an IP address, but those are the three that I'm most familiar with.

Assuming the issue is #1 or #2, the way to resolve it is to submit that unblock request by emailing AT&T's postmaster. Alternately, if you've had no response after many days, you could try sending mail to postmaster at However, if there's a reason they're not responding, because they're busy, behind, or not able to assist, pinging them again via another method isn't likely to get you a response.

It's the holiday season right now, which means lots of people are on vacation and away from work. Maybe there's a backlog of unblocking requests awaiting review and approval at AT&T. Also keep in mind that ISPs don't view their postmaster teams as the treasured and necessary resource that they once did; lots of ISPs used to have whole teams of people managing these things, and in most cases, that has been reduced to a web form and some tiny part of some single person's job. Responding to blocking requests is just not a priority for most ISPs.

And if the issue is #3, then forget about it. They'll probably just go radio silent on you, and not respond at all. Most ISPs simply don't respond to inquiries about really bad stuff. I could only theorize as to why, but if it were me, I'd figure there's no point in helping the bad guy understand how we caught him. I know that could feel unfair, because what if you're not a bad guy, and you're given no opportunity to make your case. That's just the way the world works, sometimes.

I don't see any evidence to suggest that Spamhaus is used by AT&T, nor would I make any sort of assumption that your mail would or would not be delivered to AT&T subscribers based on a Spamhaus lookup.

AT&T also publishes a postmaster site at I strongly recommend reading all the recommendations they provide there as far as best practices and how to ensure your mail is delivered successfully.

(March, 2022 Update: AT&T's "RBL Unblock" website is no more. They now tell affected senders to email, so I've updated guidance above to reflect this.)
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