Bellsouth

Bellsouth is one of the ISPs currently owned by AT&T. As of January 2010, the two properties are not completely integrated and there may be some visible differences when delivering to Bellsouth domains. One of the visible differences is that bulkfoldering for Bellsouth domains is highly correlated with bulk foldering at Yahoo.

Delivering to
There are no published limits  for connection or sending limits. There does seem to be a limit on the number of unknown users any sender can attempt, and sending to too many non-existent addresses will cause rate limiting by Bellsouth.

Postmaster pages
Bellsouth shares the AT&T 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. All of the AT&T support pages are behind a location filter. Users will need to provide a zip code to access the pages. This does not affect the information provided, so any valid zip code will do. If you are outside the US, you can use 94301 (Palo Alto, CA) as your zip.

Feedback loop
Bellsouth does not offer a FBL.

Whitelist
Bellsouth does not offer a whitelist.

Certification Services
Bellsouth uses the Return Path Certified whitelist in mail delivery decisions. Mail from IPs on the Return Path Certified list will see better delivery at Bellsouth domains.

Support for Senders
Bellsouth provides minimal support for senders. Senders who have email blocked at Bellsouth can follow the URL in the rejection message, or visit their blocking page

Known spamfilters
Not much is known about commercial spamfilters in use at Bellsouth. They do appear to be using Yahoo's reputation engine for bulkfoldering decisions, but no other information is currently available.