Cannot add previously used email to Apple Account

Review the information provided here when you request an Account Deletion:

• Can I use the primary email address for my deleted Apple Account to create a new Apple Account or with another existing Apple Account?

No, once your Apple Account is deleted, you can’t use the email address that you used with it to create a new Apple Account for as long as Apple retains the one-way hash of the email address. For third-party (non-Apple) domain accounts, the one-way hash is deleted after six years. For other accounts, this is retained according to Apple's retention policy, which is reviewed regularly. In addition, you can’t use that email address with another existing Apple Account except as a rescue email. Also, if your primary Apple Account email address is with a Custom Email Domain, it can never be reused to create an Apple Account after your Apple Account is deleted, even if the domain ownership changes.

How to delete your Apple Account - Apple Support

As for the Retention Policy of data linked to Apple Accounts that effect the deletion process, you can look here:

If you delete your Apple Account, we retain a record of the deleted account to comply with legal obligations, including as described above, and for so long as necessary for the legitimate interests of account security. If you choose to create a new account later, you will need to use an email address that is not associated with the account you have requested we delete. If you used a phone number to create your account, it cannot be used to create another account for the same reasons. You will not be able to remove the primary email address for the account or the phone number if you used it to create the account. We may also be required to retain information to comply with a court settlement or other equivalent mandated process.

Legal - Apple Account & Privacy- Apple

As for migrating accounts, Apple does provide one method for those that used an account for Media & Purchases and also a primary Apple Account, and after everything is transferred, then the account used for Media & Purchases will then be deleted.

Migrate purchases from one Apple Account to another Apple Account - Apple Support

simon0117 wrote:

How do I appeal this? There must be some way to prove I'm not trying to be malicious!

I have seen no appeal process. Apple does not put themselves in a position where they are liable for determining if an exception to a policy should be allowed by making a decision on if a user is attempting to act malicious. The best policies are those that apply to all with clear guidelines, where there are no exceptions that are determined by an employee. You certainly would not want to put that decision making on an employee where the outcome is based solely on a gut feeling and may even be inconsistent from one employee to another.

simon0117 wrote:

Note that my custom email domain is not managed by Apple/iCloud, it is third-party (Google) so it shouldn't receive a lifetime ban either according to the last sentence.

Sorry, as I was posting my comment, I saw you found the relevant section about deleting the Apple Account. Nothing in that last sentence refers to a custom email domain managed by Apple or not. The reference to the Apple Account does not mean it is managed by Apple, it refers to an account created using any custom email domain.

simon0117 wrote:

But more importantly, is there really nothing I can do now? Because I have my own custom email domain, I assume I could work around it by creating a new email/alias and adding that? No legal concerns with that?

You are correct, that juggling many different Apple Accounts is problematic, and it would be in your best interest to focus on one Apple Account and use that for Messages and Media & Purchases. For emails, you have the 3 additional ones that can be created as an alias to your Apple Account. Additional email accounts should then just be added as a mailbox to the Mail app where it is not linked to your Apple Account.

I would start fresh and you can certainly do that by creating a new Apple Account from your domain or use an existing one. If you concern is any purchases made with a different Apple Account that you want to maintain with the Primary Apple Account, use the link to migrate that data. You would need to have your Primary Apple Account signed into the device and the Secondary Apple Account signed into at Media & Purchases. That Secondary account would then be deleted after migration and no longer usable.