Sending, receiving, and organizing email in Outlook.com
Hi,
May I first ask if the deleted alias ends with @hotmail.com, @outlook.com, @live.com, or @msn.com?
If yes, once a Microsoft alias is deleted from the account, it is usually permanently removed and cannot be restored, re added, or used again to create a new account.
This is why you may see messages such as the address not being recognized while also appearing unavailable for reuse. In many cases, the address becomes permanently reserved within Microsoft systems for security and privacy reasons.
Unfortunately, Microsoft support also cannot manually recover or restore a deleted Hotmail, Outlook, Live, or MSN alias after it has been removed.
You can find Microsoft’s explanation here: https://support.microsoft.com/office/add-or-remove-an-email-alias-in-outlook-com-459b1989-356d-40fa-a689-8f285b13f1f2