Error 401 Unauthorized
Resolve authentication failures during migration.
Error Message
The remote server returned an error: (401) Unauthorized
This error indicates authentication or permission failures.
Mail Migration Causes
Office 365 Migration
Cause
Missing required Azure AD Application permissions, specifically the
full_access_as_app permission.
Solution
Add the required permissions to your Azure AD application following the Azure apps registration guide.
Exchange Migration
Username/password don't match
→ Verify by logging into Exchange server directly
Account using Multi-Factor Authentication
→ Disable MFA for the migration service account
Single Sign-On system enabled
→ Disable SSO and ensure direct Office 365 authentication
Migration account has no Exchange license
→ Assign a valid Exchange License to the account
Exchange on-prem only
→ Enable Legacy authentication in Exchange on-prem
File Migration Causes
→ Verify credentials at portal.office.com
Migration account lacks access to user's OneDrive
→ Run Preprocessing to grant access
Application cannot access OneDrive
→ Recreate connector to reinstall the application