Know about the Cutover Migration for Exchange Online (Microsoft 365).

A cutover migration is a method used to move all mailboxes from an on-premises Exchange Server to Exchange Online (Microsoft 365) in a single operation. This approach is best suited for organizations with fewer than 2,000 mailboxes, though Microsoft recommends migrating 150 or fewer for efficiency.

Some key steps in this process:

1. Verify Domain ownership: Ensure your domain is recognized by Microsoft 365.

2. Prepare Exchange server: Open necessary ports (e.g., TCP 6001, 6002, 6004 for Exchange 2003).

3. Create security groups: Set up empty mail-enabled security groups in Microsoft 365.

4. Start migration batch: Use the Exchange Admin Center to create a migration batch.

5. Monitor migration progress: Track mailbox migration status and resolve any errors.

6. Update MX records: Redirect mail flow to Microsoft 365 after migration.

7. Assign licenses: Ensure migrated users have valid Microsoft 365 licenses.

Impact on users:

• Users may experience temporary email routing delays until MX records are updated.

• Desktop computers must be configured to work with Microsoft 365.

• Users can send emails via Outlook 2013, 2010, or 2007 after setup.

Note: The Cutover Migration is a delicate process and has to some previous considerations for a detailed guide, check out Microsoft's official documentation:

Cutover Migration Method from On-Premise to Microsoft 365 - Microsoft Documentation