Change Primary Email Address of Apple ID

If you create a new iCloud address, you have created a new Apple ID. You can't merge Apple IDs.

Based on what I have read, I suggest you leave your Apple ID email address as a 3rd party email address because you have more flexibility if you need to change the email address. For example, if the Apple ID got compromised, you can change it to another address. I also have read of many people who were locked out of their accounts when they forgot their password. Since the recovery email address is the @iCloud email address, if you forget your password, you also can't access your email to get emails from Apple to recover your account. You can set a rescue email address, but for some people, this hasn't worked.

Apple IDs are either third- or first-party. A third-party account is associated with a non-iCloud email address and can be changed when you change your third-party account address. You can create one of either kind and the operating systems all support secondary accounts for various purposes (and in the worst case you can use app-specific passwords, too).

You can convert a third-party ID to a first-party one (I call this process "resignation") by enabling iCloud Mail. You cannot reverse the process (many an Apple fan learns this to their shaggrin, I find).

iCloud gives you three aliases, Hide My Email aliases, and addresses created under your own custom domains; all of these are part of the pre-existing cannon of reserved addresses that cannot be used for new Apple ID registrations.

You can rename your first-party iCloud address to another first-party address, disabling email for the original address in the process. iCloud Mail supports forwarding, so you could still receive the mail that Apple itself sends to the account (and I strongly advise doing that if you do not intend to check its email any longer for that reason). There is, in the worst case, a practical way to distance yourself from a past first-party Apple ID. But you can never dispose of an Apple ID without deleting all data associated with it. This is ultimately why many experienced Applers advise strongly against entry into the first-party purgatory of iCloud Mail on your existing Apple ID, especially if that has a lot of valuable history behind it. In your case, though, you've already taken that course, and the benefit of an iCloud email address, and since it is valuable for your Apple ID to match that address, you should simply rename your primary Apple ID. You can keep your aliases, not lose an address you will never use, and keep all your history.

Just follow the process to change your Apple ID, indicating the new iCloud address. Remember to ensure no other account under your control is laying claim to it, first.

I ran a test. At least on the surface, it now appears that you can change from first-party to third-party. I didn't complete the process, though, so I don't know how or if it affects iCloud Mail. I will soon find this out for myself, when I go back to self-hosting my own email again.

Good question!

It is known that Apple's logic forbids the creation of an email address that was once an Apple ID.

But it ought to be the case that an address that is created subsequently could become an Apple ID.

It's not the best answer. Sorry about that. But I think that's the state of play. Feedback to Apple, if you like, and demand that email addresses under domains you control ought always to be eligible as Apple IDs, even when they were previously used.

If it was a primary email, it shouldn't be getting any more email since the server should be rejecting it. If that isn't the case, go into your icloud.com Mail app, settings, Accounts; see if it has now become an alias, and get rid of it.

Since you changed the primary email, all messages should go to that address.

For the former email address, remove it from your mail app.