An Exchange migration moves mailboxes from on premises Microsoft Exchange Server to Exchange Online in Microsoft 365, or between Exchange organizations. Microsoft supports three main paths from on premises Exchange: a cutover migration that moves every mailbox at once, a staged migration for very old Exchange 2003 and 2007 servers, and a hybrid deployment in which on premises and online mailboxes coexist while users move in batches. Most mid-size and large organizations use hybrid.
This article explains how each Exchange to Office 365 migration method works and how to choose. It is part of our email migration services; for the wider program, see the Office 365 migration guide and checklist.
Exchange Server 2016 and 2019 reached end of support on October 14, 2025, and Microsoft’s on premises successor is Exchange Server Subscription Edition (SE). Organizations on older Exchange versions must either move to Exchange SE or migrate to Exchange Online. If you are staying on premises, see our Microsoft Exchange consulting and support services.
| Method | Source Exchange | Size | How it works |
|---|---|---|---|
| Cutover | 2003 to 2013 | Up to 2,000 mailboxes; Microsoft advises 150 or fewer | All mailboxes move in one batch, then DNS switches to Exchange Online |
| Staged | 2003 or 2007 | More than 2,000 mailboxes | Mailboxes move in batches; directory synchronization required |
| Hybrid | 2010 and later | Any size, typically 150 or more | On premises and Exchange Online coexist with shared address book, free/busy and mail flow; mailboxes move in batches |
| Cross-forest or cross-tenant | Exchange to Exchange, or tenant to tenant | Any | Used in mergers, acquisitions and consolidations |
Cutover is simpler: create users in Microsoft 365, migrate all mailboxes in one batch, then switch DNS. It works best for small organizations that can accept a short transition and do not need long coexistence. Users usually need a new Outlook profile afterward.
| Item | Why it matters |
|---|---|
| Public folders | Need a separate migration or a move to Microsoft 365 groups |
| Shared and resource mailboxes | Permissions, delegates and booking rules must survive the move |
| Applications and devices that send mail | Printers, scanners and line-of-business apps must relay through Exchange Online or a connector |
| Archives and PST files | Bring into online archives with retention preserved |
| Mobile devices | Profiles reconnect to Exchange Online after the move |
| Compliance | Retention, journaling and legal hold must continue without gaps |
Planning an Exchange to Office 365 migration?
RockTeam’s Exchange architects design hybrid and cutover migrations, coexistence and cutover plans for organizations from 100 to well over 100,000 users. Start with a no cost assessment.
See Email Migration ServicesMoving mailboxes from on premises Microsoft Exchange Server to Exchange Online in Microsoft 365, or between Exchange organizations or tenants.
Cutover suits small organizations on Exchange 2003 to 2013, staged covers very old Exchange 2003 and 2007 environments, and hybrid suits Exchange 2010 and later, especially for 150 or more mailboxes.
Yes. A hybrid deployment shares the address book, free/busy and mail flow, so users on both systems work normally while mailboxes move in batches.
Support ended on October 14, 2025. Organizations should migrate to Exchange Online or upgrade to Exchange Server Subscription Edition (SE) to keep receiving security updates.
Many hybrid organizations keep one Exchange server or the Exchange management tools for recipient management when identities are still synchronized from Active Directory.
