Microsoft 365 migration checklist

Before the migration

• Inventory users and mailboxes, including shared mailboxes, aliases, distribution lists and resource calendars.
• Measure data volumes for mail and files — they drive timelines.
• Map dependencies: devices, printers and scanners that send email, applications that use SMTP, line-of-business systems with mail integration.
• Check DNS access for your domains — you will need it for verification and MX changes.
• Choose licences that match what people need, including security features.

Prepare the tenant

• Verify domains and set up identities (and directory synchronisation if needed).
• Apply a security baseline from day one: multi-factor authentication, admin protection, sharing policies — see Microsoft 365 security.
• Design the SharePoint and Teams structure rather than copying old file shares as they are.
• Agree permissions for each site and team.

Migrate

• Pre-stage historical mail and files before cutover to minimise downtime.
• Pilot with a small group to test the process and support material.
• Communicate what changes, when, and what users need to do.
• Cut over in a planned window: switch MX records, update autodiscover, move sign-in.
• Final sync to catch items that arrived during the switch.

After the migration

• Hypercare: extra support for the first days while people adjust.
• Reconfigure devices and applications that sent mail through the old system.
• Validate that SPF, DKIM and DMARC are correct for the new platform.
• Decommission the old platform only once data is confirmed and retention needs are met.
• Hand over to ongoing administration — see Microsoft 365 management.