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Technically, moving from Microsoft 365 to Google Workspace is a solved problem. The Data import tool in the Admin console (Google’s current migration service, the successor of the older Data Migration Service) moves mail, calendars and contacts from Exchange Online, and it works. Projects still go wrong, almost never for technical reasons. They go wrong because nobody wrote down what “migrated” means before the switch.
What moves cleanly
- Email: mailbox history, folders and attachments, within the limits of the import tool (some item types are skipped and listed in the migration report). Slow but reliable.
- Calendars: including recurring events and attendees.
- Contacts: no drama.
- OneDrive files: Data import copies them to Drive, and Office formats open and convert in Drive. SharePoint libraries need a separate tool (Google Workspace Migrate or a third-party migration tool), so treat them as their own workstream.
Each of these has its own migration path and its own report. Check the reports for each data type separately, not one overall “done”.
What does not move, or only partly
- Excel with macros, Power Query, complex models. Sheets will not reproduce them. Keep those as Excel files in Drive and hold a few Microsoft licences for finance. Sense, not defeat.
- Outlook rules and categories. Data import now carries over some Outlook mail rules; unsupported rule types and Outlook categories stay behind. Ask each team to list the rules they rely on, then compare with the migration report and rebuild what is missing.
- Local PST archives. Anything people exported to their own disk is invisible to a server-side migration. Collect the files and import them separately, or agree in writing that they are out of scope.
- Shared mailboxes. A Microsoft concept that maps to a different answer in Google: see shared inboxes.
- Applications that depend on Outlook. Industry software that sends from Outlook, or that authenticates with a Microsoft mailbox to send mail, can stop working. Test before the switch, not after.
Where downtime hides
The moment mail can be lost is the MX record switch. Prepared properly, no mail is lost: mail starts arriving in Google while the old environment still runs, and a final sync copies the remaining supported items. Prepared badly, messages bounce or pile up in a server nobody watches.
The MX change is only one routing step, and it does not solve the rest on its own. Before the switch, SPF, DKIM and DMARC must be ready (our authentication guide covers it), DNS TTL should be lowered a day ahead, applications and devices that send mail need new credentials, and users need a plan for replacing their Outlook profile with Gmail or a reconfigured client. After the switch, verify the final sync against an inventory (users, mailbox sizes, item counts) and read the error reports rather than assuming silence means success.
A realistic timeline
- 10 to 30 users: a week of preparation, a weekend switch, a week of on-site support.
- 30 to 150: two to three weeks in waves.
- 150+: pilot first. Never everyone at once.
Four things to write down before you start
- A pilot group: five to ten users from different departments, migrated first, with a week to report problems.
- An exception register: every item that will not move (macro workbooks, PST archives, SharePoint sites, integrations) with an owner and a decision.
- An acceptance test: what “migrated” means for you, for example all mailboxes within an agreed item-count difference, calendars checked by the assistants who live in them, sign-in working on every device.
- A rollback decision: how long the old environment stays live in read-only form (30 days is a common choice), and what would make you switch MX records back during the first week.
Google’s own overview of the available tools is at Migrate your organisation’s data to Google Workspace. Checked against Google’s documentation on 10 September 2026.
The hardest part is not technical
It is people who have used Outlook for ten years. The first week brings the feeling that everything is different, and most of it is habit, not fault. One hour of training before the switch, one champion per department, a short written guide for the five tasks people do every day, and a clear message from management that the first two weeks will be slower.
Under 20 users with no Excel macros and no shared mailboxes? You can do this yourselves with Google’s documentation. More people, integrations, or no appetite for mistakes: this is a project we run regularly.
Moving mail and files to Google Workspace? We assess the sources, run a pilot, coordinate the cut-over and verify the agreed data and access afterwards. Book a free 30-minute audit or call +371 22 30 50 90.
