The sender address was rejected

I've been using iCloud, ever since dot mac.

I just recently upgraded to Sierra on the newest MBP 15.

In Mail, I get the following message "The sender address ********@mac.com was rejected by the server p32-smtp.mail.me.com" when attempting to send a message. All other devices are able to send and receive. I can receive on the MBP as well, I just can't send messages.

I have removed iCloud from my computer and re-logged in. Rebuilt mailbox. Restarted. I'm almost down to throwing away preferences, but I don't want to effect other email accounts. All has had no effect.