Fix Apple Mail's 'Invalid Email addres. Please enter a valid email address for this account' error

Having finished a recent migration to a new email server (goodbye, Linode¹) I started the process of updating my email clients. I had a wide swath of clients to update: K9 for android, Mail for iPadOS, Mail for Mac, Canary for iOS.

The Mac client setup went fine as I had not actually ever setup Mail.app on my Macbook Pro since purchasing it years ago. I had been using Thunderbird for Mac, and prior to that Canary, and prior to that MailSpring. Yes, I am unsatisfied with the state of Mac email clients.

The Problem

All these updates were going well until I started making the updates to Mail.app for iPadOS. To be clear, this is the native app that Apple provides. It gave me a clear, but also terribly wrong error message which said:

Invalid Email addres

Please enter a valid email address for this account

That seemed pretty straight forward. I must have typed the email in incorrectly right? Except the email address was valid. I never touched the email address! The thing I had updated was the mail server's hostname.

Thankfully I found the solution referenced on the Apple discussion forums.

I had created aliases for this email account and when I updated the mail server's new hostname that "Invalid Email address" error was, apparently, due to the fact that Mail.app was trying to "validate" aliases as login accounts. I put validate in quotes as no request was actually made to the mail server, so I don't know what Mail.app was actually trying to do.

The Solution

The solution was to delete all the aliases leaving only the login account. After saving the new settings I could go back and re-add all my aliases. Which is what I did.

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