Changing email address for all apple devices starting with iPad

I am attempting to change my email address for everything as the old "bellsouth" email is a mess. on my iPad I attempted to add the new email address at "sign in and security". I keep getting the message (Invalid Email

This email address is not available. Choose a different address.)? I get the same message on my old MacBook. I have to use this address as 90% of my accounts have been changed to the new address. How do get the iPad, iPhone and MacBook to accept the address?