PLATFORM

Exchange Online Migration Tool

MigrationFox handles tenant-to-tenant Exchange Online mailbox migrations: source-to-destination Microsoft 365 organizations, mergers and acquisitions, and consolidation projects. The full folder hierarchy, mail flags, categories, importance, sender attribution, and original timestamps come along with the messages. MigrationFox connects to Exchange Online through Microsoft Graph. Mail only: calendars, contacts and tasks are not migrated.

Folder Hierarchy Preservation

Exchange folders are migrated with their parent-child relationships intact. MigrationFox reads the source mailbox’s folders once, builds a destination-side folder index, and creates each new folder under the matching parent. Pre-existing destination folders are re-used rather than duplicated, so an Inbox migrated twice doesn't produce "Inbox copy" hierarchies. Folder display names handle non-ASCII characters (UTF-8 throughout).

Flag, Category, and Importance Carry

Outlook's metadata travels with each message:

• Follow-up flags: flagged messages stay flagged
• Categories: category names migrate; their colors don’t, because Outlook stores colors per mailbox
• Importance: low, normal and high are kept
• Read state: read and unread are kept
• Received date: the original date is kept, so the destination mailbox sorts the same way as the source

How MigrationFox Connects

Two ways to connect, depending on your security policy:

• OAuth2 (delegated): one signed-in user migrates their own mailbox. Lowest setup overhead.
• App-only (client credentials grant): Azure AD app registration with Mail.ReadWrite Application permission, admin consent granted. Required for bulk migrations because MigrationFox impersonates each user via /users/{upn}/messages.

Sender Attribution (app-only connection)

When migrating with app-only auth, the destination Exchange tenant doesn't let the app set the message's from field to a non-authenticated user (Graph returns ErrorAccessDenied). MigrationFox handles this by:

• Letting the destination mailbox owner become the sender recorded on the imported message
• Preserving the original sender's email as an X-Original-From internet message header so the message renders with the original "from" visible and audit fidelity is maintained

Attachment Carry

Attachments are copied through Microsoft Graph, up to 3 MB per attachment and 25 MB per message. Larger files are skipped, and an X-Migration-Note header on the message records what was left out. During the beta, attachment carry is switched on per platform as it is verified; ask about it when you request access.

Billing

Mail migration uses the same migration credit as file migrations: each message counts at its full size, including attachments. See pricing for rates.