Error: The SMTP address format is invalid , when trying to verify mailboxes to migrate.
This error occurs when trying to use the SamAccountName for mailbox login.
Please set a UPN for your users that matches their primary email address by following this procedure.
If you are using the SamAccountName ( e.g mydomain\FredSmith or just FredSmith ) currently for your users to log in then doing this will not affect your users and is easy to do.
Please check with your systems administrator for approval before making any changes.
First add a UPN domain by following the short procedure on the link below:-
Once the domain has been added you can then assign the UPN to the users using "Active Directory Users and Computers" as shown below on the screenshot.
UPN below needs to match the Primary email address.
For further asssitance with this error, please conatct our support team by raising a ticket