Suddenly can't send from Mail app

[AthenaNoctua]

Successfully sent two emails using my @me.com address. Then received a the from email is not one of your addresses error. Realising that .me is simply a redirect to @iCloud.com, I changed the domain in Mail prefs. This then gave me a
This message could not be sent because your account does not have a preferred outgoing mail server. Select an outgoing mail server from the list below.

But the only server listed in the box is iCloud - I have literally not changed anything (other than @me.com to @iCloud.com) - one second I was able to send, the next I wasn't.

Any ideas, folks? If it matters, this is an M1 Max running 12.0.1. As 12.0.1 seems to have a fair few bugs, is this another? As these emails are of critical importance, I'm going to have to log into my Webmail account and send that way. If this is a bug, does anyone know if the imminent 12.1 update will squish it?

Thanks

AN?

 

[appltech]

Hi!
According to this, everything should be hunky-dory with server requests.
Also, according to Apple, you can change or delete mail alias, and this might fix mail misbehavior but you'll lost your rare email.
Firstly, try to remove it and then add the account as a new one (but beware POP/POP3 mail accounts)