updated 01:30 pm EDT, Wed July 2, 2014
Official cutoff affecting more people than intended
Some people using @mac.com or @me.com email addresses as AIM logins in Messages are finding them non-functional, even after meeting Apple's requirements for a June 30 support cutoff, complaints indicate. In April, Apple stated that those logins would no longer work for versions of OS X below v10.7.2. Even people who do meet that threshold, however, are saying they can't use the logins anywhere, including the AIM web interface or third-party Mac and iOS clients such as Adium.
Posters on Apple's support forums have suggested various workarounds. The only surefire solution is to create a new AIM login, but this forces users to recreate their buddy lists. Apple itself hasn't commented on the matter. A quick test done with a fellow MacNN staffer's original "@mac.com" address in Messages under OS X 10.9.3 worked as expected after an initial failure.