Problems sending mail from @me.com and @iCloud.com (no problem receiving mail)

I’d set the “me” address as a “from” address in Apple Mail app, and not try reconfiguring the sending server.

See the “Set your From email address” section here: Address emails in Mail on Mac - Apple Support

crunewfs wrote:

That is exactly my problem! The @me address *is* the address I’m trying to send from (unless I’m misunderstanding you). The screenshot says “cannot send from server “me,” try sending with a different server.”

Your posting indicated “testing outgoing server”, which can be inferred to mean you’re switching sending servers.

I’d expect the same Apple iCloud sending server to tolerate messages from old email domains.

You may well have multiple outgoing servers configured.

You’ll only need entries for the servers you’re sending from.

That you can receive mail means POP or IMAP or whatever is running on the receiving server and the credentials and ports for that is all working.

The sending server is a separate entry, with SMTP or ESMTP settings, and separate credentials.