Bellsouth is one of the ISPs currently owned by AT&T. One of the visible differences is that bulk foldering for Bellsouth domains is highly correlated with bulk foldering at Yahoo.
Delivering to Bellsouth
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.
Important links and references
Bellsouth does not offer a FBL.
Bellsouth does not offer a whitelist.
Bellsouth is not currently known to support any certification services.
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 unblocking page [^1]
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.