An Office 365 migration, now usually called a Microsoft 365 migration, moves an organization’s email, calendars, contacts, archives and identities from its current platform into Microsoft 365, most often Exchange Online. The right method depends on the source system and size: Microsoft offers cutover, staged, hybrid, IMAP, Google Workspace, cross-tenant and PST import options, and larger or more complex moves use partner tooling and planned coexistence.
This guide covers how to plan and run an enterprise Microsoft 365 migration, with a step by step checklist. RockTeam delivers these projects as part of our email migration services.
| Workload | Moves to | Notes |
|---|---|---|
| User mailboxes and calendars | Exchange Online | Core of most projects |
| Shared and resource mailboxes | Exchange Online shared, room and equipment mailboxes | Permissions and booking rules must be rebuilt |
| Archives and PST files | Online archives or retention policies | Plan legal hold and retention first |
| Public folders | Exchange Online public folders or Microsoft 365 groups | Often cleaned up rather than moved as is |
| Identities and groups | Microsoft Entra ID | Usually synchronized from Active Directory |
| Files and team content | OneDrive, SharePoint and Teams | Often a separate phase |
| Method | Typical source | Key points |
|---|---|---|
| Cutover | Exchange 2003 to 2013 | Moves all mailboxes in one batch; up to 2,000 mailboxes, but Microsoft advises 150 or fewer |
| Staged | Exchange 2003 or 2007 | Batches for larger environments on very old Exchange versions |
| Hybrid | Exchange 2010 and later | On premises and online mailboxes coexist; the usual choice for larger organizations |
| IMAP | Gmail and other IMAP systems | Moves mail folders only, not calendars or contacts |
| Google Workspace migration | Google Workspace | Moves mail, calendars and contacts to Exchange Online |
| Cross-tenant migration | Another Microsoft 365 tenant | Used in mergers, acquisitions and divestitures |
| PST import | PST files | Bulk import over the network or by shipping drives |
| Partner tooling | Lotus Notes, legacy and complex sources | For platforms and requirements native methods do not cover |
For detail on Exchange sources, see Exchange to Office 365 migration; for Notes, see Lotus Notes to Office 365 migration. For other sources, see tenant to tenant migration, Google Workspace to Microsoft 365 migration and email archive and PST migration.
A migration is the best moment to raise the security baseline: enforce MFA and conditional access, configure data loss prevention and retention, and review admin roles. Many organizations involve security leadership, such as a vCISO for Microsoft 365, to approve these settings before the first wave.
See also avoiding enterprise email migration failure.
Planning a Microsoft 365 migration?
RockTeam’s migration architects plan and deliver Office 365 and Microsoft 365 migrations from Exchange, Google Workspace, other tenants and Lotus Notes, with coexistence and archives included. Start with a no cost assessment.
See Email Migration ServicesMoving email, calendars, contacts, archives and identities from an existing system, such as Exchange, Google Workspace, another tenant or Lotus Notes, into Microsoft 365, usually Exchange Online.
Yes. Microsoft renamed most Office 365 plans to Microsoft 365, so the terms are used interchangeably for the same kind of project.
Cutover suits small Exchange environments, hybrid suits larger Exchange organizations, IMAP and the Google Workspace migration handle Gmail, cross-tenant handles moves between Microsoft 365 tenants, and partner tooling covers Lotus Notes and complex sources.
From days for a small cutover to several months for a large enterprise migrating in waves. The data volume and the throughput measured in a pilot drive the schedule.
Yes. With coexistence, mail routing, free/busy and directories work across both systems until the last users move.
