AT&T
AT&T offers free email accounts for past customers at sbcglobal.net and bellsouth.net, and new and non-customers can register an att.net or currently.com free email account. AT&T provides a detailed Postmaster page with contact options for investigating false-positive spam verdicts.
Domains
att.net · sbcglobal.net · swbell.net · bellsouth.net · pacbell.net · prodigy.com
Codes
- 550↑
550 5.2.1 <EXAMPLE@PRODIGY.NET>... Addressee unknown, relay=[x.xx.xx.xx]
550 5.2.1 <example@prodigy.net>... blank mailhost - invalid address, relay=[x.xx.xx.xx]
550 5.7.1 Connections not accepted from servers without a valid sender domain. ## Fix reverse DNS for x.xx.xx.xx
Usually this is a reverse DNS (PTR) issue with the sending IP, but sometimes lookup failures by AT&T can cause this bounce to be a false-positive. After confirming reverse DNS is properly set up and the record has fully propagated, try resending the message.