What Belongs on a Migration Checklist Before You Start?
- This migration checklist starts with the facts you need. Count mailboxes and note their sizes against the Exchange Online limits.
- Choose a method. Our cutover vs staged vs hybrid guide guides your choice.
- Take a PST backup of key mailboxes.
- Clean up unused mailboxes and groups.
- Plan a message to users about the date.
What should You Set up in Microsoft 365?
- Add and verify your domain with a TXT or MX record.
- Buy and assign Exchange Online licenses. Microsoft states that unlicensed migrated mailboxes get disabled after a 30 day grace period.
- Install Microsoft Entra Connect when your method needs directory sync.
- Check that no conditional access rule blocks migrated users.
Microsoft documents Entra Connect with express settings in its minimal hybrid steps.
What should You Check on the Exchange Server?
- Outlook Anywhere works. Exchange 2013 sets it up on its own, and older versions need manual setup.
- A certificate from a trusted authority protects Outlook Anywhere and Autodiscover.
- MRSProxy is on.
- The migration admin has FullAccess on mailboxes or Receive As on the database.
- Unified Messaging is off for migrated mailboxes.
- No migrated mailbox is hidden from address lists.
These items come from the Microsoft cutover guide. Hybrid and tool based moves have their own checks.
What should You Plan for DNS?
- Lower the MX record TTL to 3,600 seconds or less before the switch.
- Plan the MX update, and wait at least 72 hours for outside systems to catch up.
- Create the Autodiscover CNAME record that points to autodiscover.outlook.com.
- Review SPF records for the new mail path.
How do You Test the Move?
Move two or three mailboxes first, as Microsoft advises in its minimal hybrid steps. Check mail, calendars and contacts in Outlook and Outlook on the web.
Fix errors in the pilot before you start the full batch.
What should You do After the Move?
- Confirm that every user receives mail in the cloud mailbox.
- Delete the cutover batch only after the Last Synced Time is later than the first direct delivery.
- Assign any missing licenses.
- Send a welcome message and help users create new Outlook profiles.
- Contact Microsoft Support before you decommission Exchange.
Use the Exchange to Office 365 Migrator when you need batches and delta sync. Our migration guide shows all four ways.
Frequently Asked Questions
What do You Need Before You Migrate to Exchange Online?
A verified domain, assigned licenses, a chosen method and a pilot plan. Directory sync is needed for some methods.
How Low should the MX TTL be?
Microsoft advises 3,600 seconds or less before the switch.
How Long should You Wait After the MX Update?
Microsoft advises at least 72 hours for outside systems to catch up.
How Many Users should You Test With?
Microsoft suggests two or three mailboxes as a test.
What Happens to Unlicensed Mailboxes?
Microsoft states that they get disabled when the 30 day grace period ends.
Do You Need Entra Connect?
Staged and hybrid methods need directory sync. Cutover needs it off during the move.
When can You Decommission Exchange?
Only after all mail flows directly to the cloud. Microsoft advises that you contact Support first.
Author's Verdict
Work the migration checklist in order, because licenses, DNS and the pilot cause most delays.
Treat the pilot as a rehearsal and fix every error before the full batch.
Key Takeaways
- Verify the domain and assign licenses first.
- Lower the MX TTL before the switch.
- Test with two or three mailboxes.
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