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1 Message

Fri, Jan 17, 2020 4:03 PM

RBL IP Unblock / Delist request

We recently encountered any issue where our email server was compromised, however, it was later resolved within a twenty-four hour period. Yet, AT&T’s email server are now blocking us and it would appear that there is no way for them to resolve it. All non-AT&T emails go through without incident except emails which are affiliated with AT&T.

The mail system

553 5.3.0 flpd600 DNSBL:RBL 521< >_is_blocked. For assistance forward this error to [email scrubbed]

I have been going through this issue for the last six weeks regarding emails being undeliverable for our email server. I have sent multiple emails to [email scrubbed]t. The reply emails from [email scrubbed]t report back that our email server is not blocked or on their blacklist. However, sending an email to anyone who has an, or, etch. immediately bounces back with the above failure.


Brand User



108.6K Messages

a month ago

Hi @BrianPDecker14,


We are delighted to help!


Let me get you in the right direction.  Please contact AT&T Postmaster to resolve your E-mail issues.


This site is intended for ISPs, email providers, and other service providers who want information about the AT&T email service, how it works, and how to resolve related issues.


Thank you for contacting us on AT&T Community Forums!


Lafayette, AT&T Community Specialist

*I am an AT&T employee, and the postings on this site are my own and don't necessarily represent AT&T's position, strategies or opinions.