I created an alias for my iCloud email address and then added it as another address I could send and receive iMessages from.
I have subsequently deleted the alias from iCloud email. However, the alias still exists as a address I can send/recieve iMessages from.
On my iPhone I can still tap the i button to get info, and remove the alias. This allows me to remove the email address from my iPhone (it claims: You will no longer be able to receive iMessages at XXX@icloud.com on any device.) However if I turn off iMessages and turn it back on the alias reappears. The alias also shows in Messages on Mac, and there doesn't appear to be anyway to remove it from Messages for Mac.
Ideally I want to permanently delete the alias from iMessage.
Best Answer
Ok – think I've sorted it. I had to remove the email address from the Manage your Apple ID: https://appleid.apple.com/signin
The email alias had become an Alternate Email address. Deleting it there removed it from iMessages after signing out and then back in.