Troubleshoot: Remove an email alias from a user
Did you get this error when you were creating a new user? "This email address is already being used as an alias for user <user name>." This article will show you how to remove the email alias from the user.
Email addresses are how the internet knows where to send your email and all email addresses must be unique - across the entire internet no two email addresses can be the same.
Remove the email address from the user
Before you begin, make sure you've noted which user you need to remove the email address from.
If you're not using the new Microsoft 365 admin center, you can turn it on by selecting the Try the new admin center toggle located at the top of the Home page.
There are two ways you can find a user's account information:
Select Manage email aliases.
Select the alias you want to remove and select the remove (wastebin) icon, and then Save changes.
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