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
- There seems to be a high correlation between bulk foldering at some domains (SBC and Bellsouth) and bulk foldering at Yahoo. These domains are not necessarily using the Yahoo MTAs, but the pattern is there. ↩
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