I have also, recently, had problems with BellSouth's servers rejecting legitimate mailing list emails to at least one user; it is not clear whether the volume is the cause, but since the server in question isn't on any of the open-relay lists, and is getting a 550 "anti-spam"ish error message, while other servers can reach the same user perfectly well...
(Note: the lists in question follow all of the relevant RFCs, including those for List-Id headers, Precedence headers, etc.)
fwiw, i already asked joel in private email to provide me with more details so that somebody can begin trying to figure out what happened. seems something's obviously wrong here. if anyone else has add'l info or similiar experiences, please shoot an email off list to me. thanks, chris