Managing personal Outlook.com account settings, security, and privacy
Hello
Only email address ending with outlook.com can be added back to its original Microsoft account.
If the email address is hotmail.com, live.com or the locale variant, like outlook.de, outlook.fr, etc. Then once removed it is permanent and cannot be added back again. Microsoft doesn't allow recycling its email addresses, so it is considered "taken" even if the address was deleted.