If you don’t get expected results when you search for email messages in the Mail app on your Mac, try these suggestions.
If a specific mailbox is selected in the Favorites bar, Mail searches only that mailbox. To search all mailboxes instead, click All.
Mail may not be looking in the Trash or Junk mailboxes or searching encrypted messages. To include them ...
In such events where a problem arises due to multiple reasons, answers look like troubleshoot efforts. Cleaning up the comments, here's what I did on Mojave for an IMAP account:
Back up the relevant folder under ~/Library/Mail/ and then delete the original folder associated with the troubling account.
Hide the ~/Library/Mail/ from Spotlight index using ...
It depends :-)
The Terminal.app itself doesn't know anything about Mail or the Internet, all (well, practically all, it can do some additional stuff but let's keep things simple) it can do is handle keyboard input and text output between the user and a so-called command shell (which on macOS usually is an application/binary called bash or nowadays zsh). So ...
There might be two things that you have to do:
It should work automatically without any intervention after the port upgrade. But to make it smooth, you might need to re-add your account in Apple Mail.
You can manually modify and add specified port too but it depends upon your email provider. However, in most cases, it should go automatically.
From apple support: You can't use a "rescue" email address to sign in to Apple. If you try to use a rescue email to sign in, you will get the error message: "This email address is not available. Choose a different address."
I had exactly this problem, and switching to my old mac.com email address fixed the problem.
I just got off the phone with Apple support for this exact question. Short answer: it can't be done.
Once you create an iCloud email account, that account can't be changed or removed from your Apple ID. The only way to delete the email account would be to delete the entire Apple ID account.