How to Migrate a Mailbox to Office 365
The right way to migrate a mailbox to Microsoft 365 depends on where the mailbox is hosted, the amount and type of data being moved, the required coexistence period, and how the final cutover will be handled. This guide organizes mailbox migration by source environment so you can choose the relevant path and then prepare, migrate, validate, and complete the transition.
This page focuses on Exchange Online mailbox data. SharePoint, OneDrive, Teams, and other Microsoft 365 workloads use separate migration workflows.
Choose the Right Office 365 Mailbox Migration Method
Start with the source system. The source determines the connection method, the data that can be moved, and the preparation required before migration.
| Source | Migration scenario | Important consideration |
|---|---|---|
| Microsoft 365 / Office 365 | Tenant-to-tenant mailbox migration | Prepare both tenants, mailbox mappings, identity/domain changes, and final cutover. |
| On-premises Exchange | Exchange Server to Microsoft 365 | Verify Exchange version, source permissions, connectivity, authentication, and target readiness. |
| Hosted Exchange | Hosted Exchange to Microsoft 365 | Confirm the provider's server, authentication, permissions, and mailbox access requirements. |
| IMAP server | IMAP to Microsoft 365 | IMAP primarily transfers email; contacts, calendars, and other data require separate handling. |
| Outlook PST | PST import to Microsoft 365 | Import depends on what the PST contains and how the source file is mapped to the target mailbox. |
Microsoft also provides native migration approaches for particular Exchange environments, including cutover and hybrid/remote moves. Select a currently supported method based on the source Exchange version and coexistence requirements rather than treating all mailbox migrations as the same process.
Before You Migrate a Mailbox to Office 365
- Confirm the source platform: Identify whether the mailbox is in another Microsoft 365 tenant, on-premises Exchange, hosted Exchange, an IMAP service, or a PST file.
- Prepare the target mailbox: Confirm that the intended Microsoft 365 user/mailbox exists where required and has the appropriate service configuration and licensing.
- Verify permissions and authentication: Confirm the administrative permissions and sign-in method required for both source and target.
- Check connectivity: Verify network access to the source and Microsoft 365 endpoints before starting a production migration.
- Review data scope: Check mailbox size, item count, folders, archive data, and any data types that need separate workflows.
- Plan the migration sequence: Decide whether users will move individually, in batches, or as part of a larger cutover.
- Plan mail flow and client changes: DNS, MX, Autodiscover, Outlook profiles, identity changes, and other cutover tasks may be separate from the data copy.
- Run a pilot when appropriate: Validate a representative mailbox before processing the wider migration scope.
How to Migrate a Mailbox to Office 365
- Prepare the source: Verify access, permissions, authentication, and the mailbox data to be moved.
- Prepare Microsoft 365: Confirm target users, mailboxes, licensing, and required configuration.
- Connect the source and target: Use the supported connection method for the selected source scenario.
- Map the mailbox: Confirm that each source mailbox or PST is associated with the correct Microsoft 365 target.
- Run the initial migration: Transfer the selected historical mailbox data.
- Run an incremental pass when required: Process supported new or changed items after the initial pass, based on the migration scenario and configuration.
- Validate the target mailbox: Review reports, folder structure, item counts where available, representative messages, calendars/contacts where applicable, and user access.
- Complete post-migration tasks: Perform required mail-flow, DNS, identity, Outlook/client, and source-decommissioning tasks only after validation.
Source-Specific Mailbox Migration Steps
The detailed procedures below retain the source-specific EdbMails workflow and screenshots for Microsoft 365 tenant-to-tenant, Exchange Server, hosted Exchange, IMAP, and PST scenarios.
Migrate a Mailbox Between Microsoft 365 Tenants
A Microsoft 365 tenant-to-tenant mailbox migration moves supported Exchange Online mailbox data from one tenant to another. Typical projects include mergers, acquisitions, divestitures, or tenant consolidation. SharePoint, OneDrive, Teams, and other Microsoft 365 workloads require separate migration workflows and should not be treated as part of a mailbox-only move.
Migration speed varies by mailbox size, item count, network conditions, source and target configuration, Microsoft 365 service limits, and concurrent workload. Plan the mailbox move separately from the final domain, mail-flow, and user cutover activities.
Steps to migrate a mailbox between Office 365 tenants
Step 1: Download and install EdbMails
- Download the installer and complete the standard Windows installation.
- Complete the setup prompts.
- Launch the app. Click Login if you've already bought, or Start Your Free Trial if you're testing first.
Step 2: Choose Office 365 migration
- Main screen → Office 365 Migration.
- Then Office 365 to Office 365 Migration.
- Job name is optional. Use the default job name or assign a descriptive job name.
- Main screen → Office 365 Migration.
Step 3: Connect the source Office 365 tenant
- Fresh connection? Add New Connection. Already got one saved? Pick it and click Connect to Existing.
- Select the supported OAuth 2.0 connection method, click Login, and complete Microsoft sign-in.
- Pick how to load the mailbox list. Check the boxes for what you're migrating. Next.
Step 4: Connect target Office 365
- For the target, select Add New Connection or choose a saved connection and click Connect to Existing.
- Choose the connection method, click Login, and complete Microsoft sign-in.
- Load the target mailbox list using the appropriate option.
Step 5: Map source and target mailboxes
- Review the automatic mapping between source and target mailboxes. EdbMails can match mailboxes using available identity attributes such as display name and email address.
- Review every mapping before migration and use manual mapping where the source and target identities do not align as expected.
Step 6: Start the migration
- Click Start Migration.
- Monitor migration progress and review the resulting logs and item counts. Use pause or resume controls where appropriate.
Need the full walkthrough with planning, prerequisites, and post-migration cutover? The Office 365 to Office 365 migration guide covers the project end-to-end.
Migrate a Mailbox to Office 365 from Exchange Server
For on-premises Exchange, the appropriate migration approach depends on the Exchange version, organization design, coexistence requirements, and target Microsoft 365 configuration. EdbMails can connect to supported Exchange environments and migrate selected mailbox data directly to Microsoft 365.
Before starting, verify source connectivity and permissions, prepare the target mailboxes and licenses, confirm authentication, and decide how mail flow and user access will be handled during the final transition.
Steps to migrate a mailbox from on-premises Exchange
Step 1: Install and launch EdbMails
- Get EdbMails installed on a Windows machine.
- Launch the app. Click Login or Start Your Free Trial.
- Pick Live Exchange Migration → Live Exchange to Office 365 Migration.
Step 2: Connect the source Exchange server
- Brand new connection? Add New Connection. Got one saved? Connect to Existing.
- Drop in the connection details. Sign in.
- Load the mailbox list automatically or by CSV, as appropriate. Tick what you're migrating. Next.
Step 3: Connect target Office 365
- Add New Connection on the target side, or Connect to Existing for saved.
- Authentication method. Click Login. Sign in at Microsoft's page.
- Auto-load or CSV-load the mailboxes. Next.
Step 4: Map Exchange to Office 365 mailboxes
- Confirm that the required target mailboxes and licenses are ready. Where supported and configured, use the available mailbox-creation and mapping options.
- Review the automatic mapping and override it manually when source and target identities do not align.
Step 5: Start the migration
- Click Start Migration.
- Monitor the migration and review the migration report when processing completes.
- Validate the target Microsoft 365 mailbox, including expected folders and representative items.
Migrate a Mailbox to Office 365 from Hosted Exchange
Hosted Exchange migrations require access to the source provider and an appropriate connection method. The exact prerequisites vary by provider, so confirm the hosted Exchange server address, authentication requirements, permissions, and mailbox access before starting.
Prepare the Microsoft 365 target in advance, map each source mailbox to the intended target mailbox, and validate migrated data before changing mail flow or user access.
Steps to move hosted Exchange to Office 365
Step 1: Install and launch EdbMails
- Install EdbMails on a supported Windows system.
- Open EdbMails and select Login or Start Your Free Trial.
- Main screen → Live Exchange Migration → Hosted Exchange to Office 365 Migration.
- Use the default job name or select New Job to create a descriptive job name.
Step 2: Connect the source hosted Exchange server
- Select Add New Connection for a new connection, or choose a saved connection and click Connect to Existing.
- Choose Connect to Hosted Exchange server. Next.
- Two ways to actually connect, depending on what your hosted provider exposes:
- Autodiscover Email – uses provider Autodiscover where available. Email and password, the provider's Autodiscover handles the rest.
- Default Connection – lets you specify the server address directly. Drop in the server's FQDN or IP directly.
- Moving multiple mailboxes? Use the Full Access permission option, then Next. Use this option only when the required permissions are available for the selected mailboxes.
- Enter the source hosted Exchange credentials and sign in.
- Load mailboxes — auto-load or CSV. Tick the ones you want. Next.
Step 3: Connect target Office 365
- For the Microsoft 365 target, add a new connection or select a saved connection.
- Select the supported OAuth connection method and complete Microsoft sign-in.
- Auto-load or CSV-load for target mailboxes. Next.
Step 4: Map hosted Exchange to Office 365 mailboxes
- Review the automatic source-to-target mailbox mapping.
- Use manual mapping where a source mailbox or folder requires a specific target.
Step 5: Start the migration
- Click Start Migration to begin processing the selected hosted Exchange mailboxes.
- Monitor the migration progress.
- When processing completes, select View Logs and review the migration report.
- Sign in to Microsoft 365 and validate the migrated mailbox folders and representative items.
Migrate a Mailbox to Office 365 from an IMAP Server
IMAP is suitable when the source is an IMAP-enabled service such as Gmail, Zoho Mail, Zimbra, IceWarp, cPanel, or another compatible mail platform. An IMAP migration primarily transfers email messages and folders; contacts, calendars, tasks, and other non-email data require separate handling.
Confirm the source IMAP host, port, encryption and authentication requirements before migration. For bulk moves, validate a small pilot group before processing all users.
Steps to migrate a mailbox from an IMAP-enabled server
Step 1: Download and install EdbMails for IMAP migration
- Install EdbMails on a supported Windows system.
- Review the system requirements before starting a large or bulk migration.
- Sign in with email and password, or Start Your Free Trial for trial mode.
- Pick IMAP (Gmail, Outlook & more) Migration.
- Then IMAP to Office 365 Migration from the menu.
- Use the default job name or create a descriptive job name.
Step 2: Connect the source IMAP server
Single mailbox? Pick Single User / Account Migration:
- Choose the protocol supported by the source. Connect to IMAP Server or Connect to POP3 Server.
- Enter the server details and account credentials using the authentication method required by the source provider. For Gmail and other providers, follow the provider's current OAuth or app-password requirements where applicable.
- Click Login.
Bulk migration instead? Pick Multiple (Bulk) Users/Accounts Migration:
- Download the sample CSV file.
- Enter the required account, host, port, and authentication details for each user, then save the CSV.
- Select Browse CSV File, choose the completed CSV, verify the mailbox list, and continue.
- Choose the protocol supported by the source. Connect to IMAP Server or Connect to POP3 Server.
Step 3: Select source IMAP mailboxes
- Select the required mailboxes or folders and continue.
- Select the required mailboxes or folders and continue.
Step 4: Connect target Office 365
- For the Microsoft 365 target, add a new connection or select a saved connection and click Connect to Existing.
- Connection options, then Next.
- Select OAuth 2.0 where applicable, click Login, and complete Microsoft sign-in.
- Pick a method to load the mailboxes.
Step 5: Map source and target mailboxes
- Pick a mapping option.
- Review mailbox and folder mapping carefully. Confirm that required target mailboxes are provisioned and licensed before migration.
Step 6: Start the IMAP migration
- Click Start Migration.
- Monitor migration progress.
- When processing completes, select View Log and review mailbox and folder-level results.
Migrate Mailbox Data to Office 365 from an Outlook PST File
PST import is useful for archived Outlook data, former-user mail, or mailbox data exported from another environment. A PST can contain email, calendar, contact, task, and other Outlook items; the data available for import depends on what is stored in the PST and what the target import workflow supports.
Before importing, confirm that the PST files are readable, identify the intended target mailboxes, and review how source folders should map to the destination.
Steps to move PST files into Office 365 mailboxes
Step 1: Install EdbMails
- Install EdbMails and review the system requirements before processing large or multiple PST files.
Refer to the system requirements for importing multiple PST files to Office 365.
- Install EdbMails and review the system requirements before processing large or multiple PST files.
Step 2: Launch and choose the migration type
- Open the app. Email and password to sign in, or Start Your Free Trial.
- Dashboard → Office 365 Migration
- Then Restore PST to Office 365.
- Use the default job name or create a descriptive job name.
Step 3: Add multiple PST files
- Select Add File(s), browse to the PST location, and choose the files to import.
- Verify that the required PST files appear in the list.
- Optional: turn on the setting that creates a target folder named after each source PST. This can help separate multiple source PSTs within the same target mailbox.
- Next when you're done.
- Select Add File(s), browse to the PST location, and choose the files to import.
Step 4: Connect target Office 365
- For the target, add a new connection or select a saved connection.
- Connection method, then Next.
- Complete Microsoft sign-in.
- Choose the appropriate method to load target mailboxes, such as manual selection or CSV.
Step 5: Map PSTs to Office 365 mailboxes
- Choose the appropriate mapping option.
- Review the automatic mapping between PST files and target Microsoft 365 mailboxes.
- Use manual mapping when file names and target mailbox identities do not align.
Step 6: Start the PST import
- Click Start Restore.
- Confirm the completion status.
- Open View Log and review the migration report.
How to Minimize User Disruption
Mailbox data transfer and final service cutover are separate stages. Where the migration scenario permits it, historical data can be moved before the final transition, and a later incremental pass can process supported new or changed items. This can reduce the amount of data remaining at cutover.
Incremental migration should not be treated as a substitute for validation. Review migration reports after each pass and confirm that the target mailbox contains the expected data before changing mail flow or moving users to the new environment.
The final transition may still require DNS or MX changes, identity updates, Outlook or mobile-client reconfiguration, and other environment-specific work. The amount of user interruption therefore depends on the source, migration architecture, and cutover plan.
Common Office 365 Mailbox Migration Issues
| Issue | What to check |
|---|---|
| Source connection fails | Server address, network access, authentication method, permissions, and service availability. |
| Target mailbox is unavailable | User provisioning, Exchange Online licensing/service configuration, and target mailbox readiness. |
| Mailbox mapping is incorrect | Source and target identities, UPN/email changes, manual mappings, and consolidation requirements. |
| Migration is slower than expected | Mailbox size, item count, network performance, Microsoft 365 service limits/throttling, source performance, and concurrent workload. |
| Some data types are missing | Confirm what the selected source protocol can migrate. IMAP, for example, primarily handles email. |
| Users cannot connect after cutover | Mail flow, DNS/MX, Autodiscover, identity, Outlook profiles, licensing, and client configuration. |
Using EdbMails for Mailbox Migration
EdbMails provides source and target connection, mailbox selection and mapping, migration execution, incremental processing for supported scenarios, and migration reports within the application workflow. For the broader product capabilities and supported migration directions, see the Office 365 migration Tool.
Use this page to choose the source-specific mailbox workflow. Use the parent product page for broader Office 365 migration capabilities rather than treating this support article as a product comparison or pricing page.
Related Mailbox and Microsoft 365 Workloads
Mailbox migration is only one workload. If the project includes archive or public-folder data, use the workload-specific procedures rather than assuming the mailbox steps cover those objects. For an archive mailbox moving from Microsoft 365 to Exchange, refer to the office 365 archive mailbox to exchange guide. For public folders moving between Microsoft 365 environments, use the office 365 public folder migration to office 365 guide.
Frequently Asked Questions
How do I migrate a mailbox to Office 365?
Identify the source platform, prepare the Microsoft 365 target, confirm permissions and authentication, connect the source and target, map the mailbox, run the migration, validate the target, and then complete any required mail-flow or client cutover tasks.
Can I migrate a mailbox from one Microsoft 365 tenant to another?
Yes. A tenant-to-tenant migration moves supported Exchange Online mailbox data between Microsoft 365 tenants. The project also requires source/target preparation and separate planning for identity, domain, mail-flow, and user cutover requirements.
Can I migrate an Exchange mailbox to Office 365?
Yes. The appropriate path depends on the Exchange version, coexistence requirements, source connectivity, permissions, and target configuration. Validate the supported migration method for the source environment before starting.
Can I migrate an IMAP mailbox to Office 365?
Yes. IMAP can be used to migrate email messages and folders from compatible mail systems. Contacts, calendars, tasks, and other non-email data generally require a separate migration or export/import workflow.
Can I import a PST into an Office 365 mailbox?
Yes. A PST can contain email, calendar, contact, task, and other Outlook items. What is available for import depends on the PST contents and the target import method.
Does mailbox migration require a final cutover?
Often, yes. The data copy can be performed before the final transition, but DNS/MX, identity, mail-flow, Outlook/client, or domain changes may still be required depending on the migration scenario.
How do I verify that a mailbox was migrated successfully?
Review the migration report, validate the target folder structure and item counts where available, open representative messages and attachments, check calendar/contacts when applicable, and confirm that the user can sign in and send and receive mail after cutover.
