Adding Sandbox Tester in iTunes Connect with an existing Apple account

Question

I\'m trying to add sandbox testers in iTunes Connect. But I\'m getting this error:

The email address you entered already belongs to an existing Apple acco

Answer 1

The errors

The email address you entered already belongs to an existing Apple account. Please try again.

and

An unknown error has occurred.

and

An error has occurred. Try again later.

are equivalent.

It means that your email address is not accepted. The email field may also be highlighted red when the error message is shown.

Apple blocks these email addresses (this is undocumented):

• Existing Apple accounts
• Existing Apple accounts with the Gmail + trick added to the sandbox user account
• Mailinator
• Mailinator alternate domains
• Other, undocumented stuff

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I'm just going to post the real solution here, since this is what other people are wanting to know:

ANSWER

1. Login to MyDomain, or GoDaddy or whatever you use to manage your personal domain (if you don't control any domains you can turn in your nerd card now)
2. Create a new MX record for anon.yourdomain.com and point it to mail.mailinator.com. Or, possibly, realize that you already did this a while ago for some previous reason
3. Register the sandbox with some email like appleserrormessagessuck@anon.yourdomain.com
4. Then you're done