As announced on their Postmaster Blog by Lead Postmaster Lili Crowley.
I think it's fair to assume that the legacy AOL Postmaster site is likely to shut down at some point in the near future. It brings a tear to my eye, as that site goes back quite a long time. Here it is in 2003, courtesy of the Internet Archive.
March 2022 Update: Now that Yahoo is just Yahoo again, Yahoo's Senders Hub (postmaster) website can now be found over here at https://senders.yahooinc.com .