Email Migration

What Migrates from Exchange Server 2019 to Exchange Online?

Olivia Miller Oct 9, 2026 869 views

Question details

Understanding which data, settings, and external components are transferred when migrating from Exchange Server 2019 to Microsoft 365 Exchange Online.

What Migrates from Exchange Server 2019 to Exchange Online?

Product: Microsoft Exchange Server 2019
Device & OS: not provided
Scenario: Planning a mailbox and server migration to Microsoft 365.
Observed behavior: Users need to clarify if mailbox rules, directory objects, groups, calendar sharing, and external gateways like SMG will automatically migrate.

Before you start

Identify your specific migration method (such as cutover, staged, or hybrid) before beginning, as the method dictates which mailbox settings and rules are automatically transferred.

Solution 1Recommended

Review and Manage Migrated Mailbox Components

Understand how mailbox data, rules, groups, and external systems are handled during the Exchange migration process.

While standard mailbox data typically migrates smoothly to Microsoft 365, secondary configurations such as mail-flow systems, distribution groups, and specific calendar permissions often require manual intervention.

Check Mailbox Rules and Policies

Verify how your chosen migration method handles inbox rules and policies. Some standard rules migrate automatically, but complex organizational policies may require manual recreation in the Exchange Admin Center.

Synchronize Directory Objects and Groups

Use Microsoft Entra Connect (formerly Azure AD Connect) to properly synchronize your on-premises directory objects and distribution groups to Microsoft 365, or recreate them manually if you are performing a cutover migration.

Configure Calendar Sharing

Review calendar sharing permissions across your organization. If you are operating in a hybrid environment, you may need to configure specific organization relationships to maintain cross-premises calendar sharing.

Integrate External Mail Components

Note that external mail-flow components, such as a Secure Mail Gateway (SMG), do not migrate automatically. You must manually update your MX records, configure inbound/outbound connectors, and integrate the gateway with Exchange Online separately.

Review and Manage Migrated Mailbox Components

Migration Methods Matter: The exact migration outcome always depends on the specific path you choose (e.g., minimal hybrid, full hybrid, or cutover). Always consult the official Microsoft Exchange mailbox migration documentation for your specific setup.

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Frequently Asked Questions

Does a Secure Mail Gateway (SMG) automatically migrate to Exchange Online?

No, a Secure Mail Gateway is an external mail-flow component. It does not migrate automatically; you must manually integrate it with Exchange Online by configuring the appropriate mail flow connectors.

Will my distribution groups transfer during the migration?

Distribution groups and directory objects require proper synchronization using Microsoft Entra Connect. If you are not using synchronization tools, you will need to recreate them manually in Exchange Online.

Do calendar sharing permissions remain intact after migrating to Microsoft 365?

Internal calendar permissions typically migrate with the mailboxes. However, if you are running a hybrid setup during the migration, calendar sharing between on-premises and Exchange Online users will need to be configured separately via organization relationships.