You cannot let two Exchange mailboxes using the same email address. If you want to use the email address for a new mailbox, you need to remove or disable the old mailbox, after that, you could use that old email address for a new Exchange mailbox.
If the response is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.