ODM Mailbox Migration Error: No valid accounts specified for mail migration (4378147)

The mail migration task is failing with the following errors:

• No valid accounts specified for mail migration
• Mail migration failed because the target user does not have a license for a mailbox

What Has Been Confirmed:

• The account is properly licensed. For shared mailboxes, a mailbox license is not required. 
  • https://support.quest.com/kb/4350366/user-mailbox-migration-task-failed-error-no-valid-accounts-specified-for-mail-migration
• In the ODM Accounts tab, the Type field is populated for both the source and target accounts.
• The Refresh Account task has been run after the domain move and completed successfully.

The source domain has already been moved to the target tenant. However, the source mailbox retains the same primary SMTP address, which results in both the source and target mailboxes having identical primary SMTP addresses.

Update the primary SMTP address in the source to a domain that has not yet been migrated to the target. Typically, this would be the onmicrosoft.com domain.