Hello @JenniferP0 ,
The issue is that the email address is being used as a username on the other accounts, and not something related to MFA. Nevertheless, it is a security and compliance requirement that users have their own unique logins for each account they're logging into. If you're finding that a user you're trying to add already has their email in use, then they'll need to login to the account where that email is currently the username, and update the username for that account to not be their email.
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