In a April post to the Mac OS X Server Mailing List, moderator Conrad Klahn said that the mailing lists run by Apple would be transitioned to read-only mode at the end of April and afterwards, no new subscriptions or posts would be accepted. It would continue as an archive.
Moving forward, Apple will be providing discussions in two different areas: Apple Support Communities and Apple Developer Forums.
Discussions for Servers and Enterprise Software are available here.
It has been my honor to provide support to this list since 1998 when we first introduced Mac OS X Server to Apple customers. Your support of Apple, OS X Server and this list is greatly appreciated.
However, a number of the discussion mailing lists appear to still be functioning, including the Client Management Mailing List and the Xcode Users List. I notice that the Darwin Kernel List stopped at the end of April and there are no new posts, which is unusual.
These discussion mailing lists are very old school. I subscribe to a number of them and they fit in my workflow, putting the content where my eyeballs are most of the day: my mailbox. This is either the end of an era or it isn't. I can't tell.
Is it another warning sign for OS X Server? No idea.