How Migrate domain emails

Choose the migration method from the current mail platform first, migrate and validate mailbox data, and only then change the domain’s MX record to route new mail to Exchange Online.

1. Confirm administrative access

You need:

• Microsoft 365 and Exchange administrator access.
• Access to the existing mail system or credentials for its mailboxes.
• Permission to edit the domain’s public DNS records at its registrar or DNS host.
• Microsoft 365 licenses that include Exchange Online.

Do not cancel the existing mail service or change its MX record yet.

2. Add and verify the customer’s domain

In the Microsoft 365 admin center:

1. Select Show all → Settings → Domains.
2. Select Add domain.
3. Enter the customer’s public domain, such as contoso.com.
4. Add the TXT verification record displayed by Microsoft 365 at the DNS host.
5. Return to the wizard and complete verification.

Domain verification establishes ownership; it does not move existing email or redirect incoming messages.^1^

3. Select the migration method

Microsoft supports different methods according to the source system.^2^

Hosted email or another IMAP provider

Use an IMAP migration if the current provider supports IMAP:

1. Create each Microsoft 365 user and assign an Exchange Online license so the destination mailbox exists.
2. Obtain the source IMAP server details and either administrator access or each mailbox’s credentials.
3. In the Exchange admin center, open Migration and create an IMAP migration batch.
4. Supply the requested CSV containing mailbox addresses, source usernames, and credentials.
5. Start the batch and verify its synchronization status.

IMAP copies email folders only—not contacts, calendars, or tasks. It supports up to 500,000 items per mailbox and messages up to 35 MB.^3^

For Google Workspace, use Microsoft’s Google-specific migration path rather than generic IMAP when calendar or contact migration is required.

On-premises Exchange Server

Choose according to the Exchange version, mailbox count, and coexistence requirement:

• Exchange 2010, 2013, or 2016; approximately 150 mailboxes or fewer; move everyone quickly: cutover or Minimal Hybrid.
• More than 150 mailboxes, phased migration, or coexistence: Exchange Hybrid.
• Exchange 2010 IMAP: do not use it; its TLS implementation is incompatible with Exchange Online. Use cutover, hybrid, or PST import instead.^4^
• Staged Outlook Anywhere: do not begin a new staged onboarding; it was retired on May 8, 2025.^5^

For an Exchange cutover migration, do not manually pre-create duplicate users and mailboxes. The migration creates them from the on-premises mailbox objects; assign their Exchange Online licenses after migration synchronization.

Before creating the cutover endpoint, verify:

• Directory synchronization is not enabled.
• Outlook Anywhere and Autodiscover are available with a trusted certificate.
• MRSProxy is enabled.
• The migration account has FullAccess on each mailbox or Receive As on the mailbox database.
• Migrating mailboxes are visible in address lists.

Then go to Exchange admin center → Migration → Endpoints, create the endpoint, create the cutover migration batch, start synchronization, and validate the migrated mailboxes.^6^

4. Perform the DNS cutover

Only after every required recipient exists in Exchange Online and migrated data has been validated:

1. Run or wait for the final synchronization.
2. Open Microsoft 365 admin center → Settings → Domains → select the domain → DNS records → Manage DNS.
3. Add Microsoft’s displayed MX, Autodiscover CNAME, and SPF records.
4. Remove the former provider’s MX record, or ensure Microsoft 365’s MX record is the preferred record according to the DNS provider’s priority convention.
5. Test inbound and outbound mail for several users.

Changing the MX record sends new mail to Microsoft 365; existing mail remains at the old provider unless it was migrated separately.^7^

Keep the old service and migration batch available until mail flow and final synchronization are confirmed. MX changes can take up to 72 hours to be recognized globally.^6^

References

1. Add a custom domain to Microsoft 365
2. Decide on a migration path in Exchange Online
3. What you need to know about migrating your IMAP mailboxes to Microsoft 365 or Office 365
4. Can't migrate IMAP mailboxes from Exchange Server 2010 to Exchange Online
5. Perform a staged migration of email in Exchange Online
6. Migrate email to Exchange Online using the Exchange cutover method
7. Connect your domain by adding DNS records