Exchange Web Services reported that an SMTP email address cannot be resolved to a user/mailbox. The offending email address could be that of the end user or the admin account (if using admin credentials).
Check the error to determine if it was reported for the Source or Destination system.
Check that the email address is correct. Very often, we will find that this error is due to a typo.
- Log in to OWA using any user account (example: an admin account).
- Compose a new email draft.
- On the TO line, copy/paste the exact same email address that has been specified in the migration configuration.
- Click on the Check Names button to see if the email address resolves to a user/mailbox in the address book.
- Do this for both the user account and the admin account.
If migrating from or to Office 365 (and not using impersonation), check that the admin account has been assigned a license.
- Log in to http://portal.microsoftonline.com as admin.
- Assign a license to the admin account.
- Wait for 30 minutes to allow for the mailbox to be created.
- Resubmit the mailbox for migration.
In a few rare cases, we find that the user has been hidden from the address book, and so the email address cannot be resolved in the address book. In other rare cases, the address book has not been rebuilt to include recently created mailboxes, and so cannot resolve a valid email address.