O365 Migration: map users for Teams & Groups

How owners, members and message authors are matched to destination users, with a CSV, automatic matching and an "Unresolved users" account.

How a user is matched

O365 Migration tries these in order for every owner, member, channel member and message author:

1. Your mappings: Source,Destination pairs (user principal names or e-mail addresses).
2. Same address: a destination user with the same user principal name or e-mail address.
3. Same name at a domain: name@ the domain you choose, for example jane.doe@contoso.com → jane.doe@fabrikam.com.
4. Unresolved users: everyone else is added as this account.

Turn off Match users automatically to use only your mappings and the Unresolved users account.

Users CSV

Source,Destination
jane.doe@contoso.com,jane.doe@fabrikam.com
old.alias@contoso.com,new.alias@fabrikam.com

Open Migrate → Edit user mapping → Import CSV. Export creates the same format.

The Unresolved users account

• Recommended: a service account such as migration@fabrikam.com.
• Messages written by unmatched people are imported under this account, and still show the original author's name.
• It is added as a member, never as an owner. A team needs at least one matched owner, or the Unresolved users account, to be created.
• Without it, unmatched members are listed as warnings in the report, and their messages are not imported.

Updated 2026-10-17