Action: When you migrate on-premises Exchange mailboxes to Office 365, certain permissions to access and, in some cases, ...

Action: When you migrate on-premises Exchange mailboxes to Office 365, certain permissions to access and, in some cases, modify those mailboxes, are required. The user account used to connect to your on-premises Exchange organization during the migration needs those permissions. Learn more at Assign Exchange permissions to migrate mailboxes to Office 365.