Migrate Gmail to Microsoft 365 Without Losing Email

Q: Will I lose email when migrating from Gmail to Microsoft 365?

Not if the migration is staged properly. Mailboxes are copied into Exchange Online while staff continue using Gmail, then the domain's MX record is switched at a quiet time and a final incremental sync captures anything that arrived during the change. Keep the Google subscription active for a few weeks afterward as a safety net before cancelling it.

Q: How long does it take to migrate Gmail to Microsoft 365?

A 10-person office with typical mailboxes usually takes about two weeks from kickoff to cutover, most of which is background copying. Offices of 50 to 100 users with large Shared Drives commonly need four to six weeks. The actual cutover interruption is minutes. Delays usually come from decisions about folder structure or from third-party systems that send mail through your domain.

Q: Does Google Drive move to Microsoft 365 too?

Yes. Personal My Drive content moves to each user's OneDrive, and Shared Drives map to SharePoint document libraries. Google Docs and Sheets convert to Word and Excel during the copy. Review complex spreadsheets, forms, and scripts afterward, and expect old sharing links to stop working, so anything embedded in your website or sent to clients must be re-shared from the new location.

To migrate Gmail to Microsoft 365 without losing email, you license Microsoft 365 first, add your domain to it while leaving DNS pointed at Google, copy every mailbox, calendar, and contact list into Exchange Online while staff keep working in Gmail, then switch DNS at a quiet moment and let a final delta sync catch anything that arrived during the switch. Done in that order, nothing is lost and the visible interruption is measured in minutes.

Why businesses migrate Gmail to Microsoft 365

Most of the Treasure Coast businesses we move come from one of three situations: they started on free or consumer Gmail accounts and need a real business domain with central control; they use Google Workspace but their industry lives in Excel, Word, and Outlook and the friction has become constant; or a compliance requirement such as HIPAA, a cyber-insurance questionnaire, or a client's security review is easier to satisfy with Microsoft's business tiers. Whatever the reason, the migration mechanics are the same.

Step 1: Inventory before you touch anything

The migrations that go badly are the ones nobody mapped. Before licensing anything, list:

Every user mailbox, including part-time staff and seasonal employees who may be inactive right now.
Shared mailboxes and Google Groups used as addresses such as info@ or billing@.
Aliases and forwarders, which are easy to forget and painful to discover after cutover.
Shared calendars, resource calendars for conference rooms, and delegated access.
Google Drive contents, especially Shared Drives, and who owns which folders.
Third-party systems that send mail through your domain: practice management software, the website contact form, the copier, the accounting system, and any marketing platform.
Mailbox sizes. A 40 GB mailbox with a decade of attachments takes hours to copy and should be started first.

Step 2: Choose licensing and set up the tenant

For most 5 to 250 person businesses, Microsoft 365 Business Basic, Standard, or Premium is the right family. Business Premium includes the security and device management features that insurers and regulated industries ask about, and it is what we recommend for medical, legal, and financial firms. Set up the tenant, add your domain, and verify it with a single TXT record. This does not affect mail flow; Gmail keeps receiving everything. Create the users, assign licenses, and configure multi-factor authentication before anyone signs in for the first time. Migrating an insecure setup is a missed opportunity.

Step 3: Migrate mailboxes while staff keep working

Microsoft's built-in Google Workspace migration copies mail, calendar, and contacts from Gmail into Exchange Online using a service account you authorize in the Google admin console. It runs in the background, and staff continue using Gmail as usual. For larger or more complex tenants, or when you need detailed reporting and retry control, a third-party migration tool is worth the modest cost.

Run the initial pass days before cutover. It copies the bulk of the data. Then leave the migration batch open so incremental syncs pick up new messages every day. Review the reports: mailboxes that show skipped items usually have oversized attachments or malformed messages, and it is far better to find those now than after the switch.

Two things do not migrate cleanly and need a plan. Gmail labels become folders, so a message with three labels shows up in three folders, which surprises people. And Gmail's conversation view has no exact equivalent; staff used to it need ten minutes of orientation in Outlook.

Step 4: Move Drive to OneDrive and SharePoint

This is often bigger than the email piece. Personal My Drive content goes to each user's OneDrive. Shared Drives map naturally to SharePoint document libraries, typically one per department or team. Native Google formats such as Docs and Sheets are converted to Word and Excel during the copy. The conversion is good but not perfect: complex Sheets formulas, Google Forms, and scripts need review, and shared links from the old environment stop working, so anything embedded in your website or sent to clients must be re-shared.

Use the migration window to fix structure. Ten years of Drive sprawl does not need to be copied as-is. Agree on a simple SharePoint layout and permission model before the copy, and archive what nobody has opened in two years.

Step 5: Time the cutover

Cutover is the moment you change the MX record so new mail arrives in Microsoft 365. The best time is Friday evening or Saturday morning for a standard office, or the slowest afternoon of the week for a medical practice with weekend hours. A cutover checklist looks like this:

Lower the DNS time-to-live values a day ahead so the change propagates quickly.
Run a final incremental sync of all mailboxes.
Change the MX, SPF, DKIM, DMARC, and autodiscover records.
Update every third-party system that sends mail through your domain to use the new SMTP settings or a proper relay.
Run one more sync a few hours later to catch anything that arrived at Google during propagation.
Test inbound, outbound, and internal mail, calendar invites, and a shared mailbox.

Keep the Google subscription active for two to four weeks as a safety net, then export a final archive before cancelling.

Step 6: Set up devices and train staff

Configure Outlook on desktops and the Outlook mobile app on phones, remove old Gmail accounts from devices so people do not keep replying from them, and walk everyone through where their files landed. Half an hour of group training prevents a week of help desk tickets. Our Microsoft 365 migration service includes this session because it is where most of the perceived success of a migration is decided.

How long does a Gmail to Microsoft 365 migration take?

For a 10-person office with modest mailboxes, plan on about two weeks from kickoff to cutover, with most of that time being background copying and scheduling. Offices of 50 to 100 users with large Shared Drives typically take four to six weeks. The migration itself is rarely the bottleneck; waiting on a decision about folder structure or on a vendor to update SMTP settings is.

Post-migration cleanup people forget

Turn on third-party Microsoft 365 backup; Microsoft does not back up your tenant for you.
Configure retention and litigation hold if your industry requires it.
Convert forwarders to shared mailboxes or distribution groups so mail is not silently lost when someone leaves.
Review external sharing settings in SharePoint, which default to more open than most offices want.
Remove the Google migration service account and revoke its access.

Migrations are routine for us and stressful for you, which is exactly why you should not do one alone. MainSail Data plans and runs Gmail to Microsoft 365 migrations for businesses across Vero Beach, Fort Pierce, Port St. Lucie, and Stuart. Call (772) 794-1194 or contact us for a free migration assessment and a fixed-scope quote.

Migrate Gmail to Microsoft 365 Without Losing Email Microsoft 365 · 6 min read