AT&T

AT&T owns a number of domains, including SBC and Bellsouth. Some AT&T domains also use Yahoo filtering rules to send mail to the bulk folder¹.

Delivering to AT&T

There are no published limits for connection or sending limits. I have seen claims of limits of 2 connections per IP and 30 connections per IP, but there has been no data presented for either claim.

Important links and references

Postmaster pages

AT&T provides postmaster pages with information about bounce codes and blocking. They also provide information for other receiving sites, including a list of their outgoing SMTP servers.

Feedback loop

AT&T does not offer a FBL.

Whitelist

AT&T does not offer a whitelist.

Certification Services

AT&T uses the Return Path Certified whitelist in mail delivery decisions. Mail from IPs on the Return Path Certified list will see better delivery at AT&T domains.

Support for Senders

AT&T provides minimal support for senders. Senders who have email blocked at AT&T can follow the URL in the rejection message, or visit their SMTP errors list
AT&T also provides as block inquiry website. Block Inquiry Form

Known spamfilters

AT&T does not publish any specifics on what blocklists they use. Their email best practices page suggests that sending IPs should not be on any Real-time Blackhole list[sic] and that they may block mail listed on any reputable list.

Notes

Updated 3/12/2014