I have been using a mac mail alias as my iMessage and FaceTime apple ID without any problems. Yesterday I noticed I was logged out of iMessage on my iPad. I went to log back in but it wouldn't accept my ID and password and after three attempts it took me to the retrieve password page.
There I entered my firstname.lastname@example.org ID and received the message 'This person record is inactive!!! I went to my iPhone and was happily
Ogled in in iMessage with that ID. I sent some messages just to check and all was fine.
I then tried on my ipad to log in using another Apple ID - that was fine - and then tried to add the 'problem' email address - which was there but was showing as unverified. This generated a 'email associated with multiple IDs - please delete or contact Apple Support'. I went to delete it and got the same message. I tried to add a different email and got the same message. Basically I am unable to change anything associated with my email@example.com Apple ID because the firstname.lastname@example.org email is associated with multiple accounts.
I then went into my (working) iPhone iMessage account and it asked for my password. As you all probably know, you then end up being unwittingly logged out of something you thought you were logged in to and so I am now unable to access iMessage on my primary (albeit an alias!) email address because Apple on the on hand tell me that it's an inactive person record and on the other that the email address is associated with multiple IDs (but won't let you do anything to remedy that).
In summary: I'm now no longer accessible by iMessage & FaceTime....