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Migrating to Microsoft 365: How It Actually Works
Most migration horror stories — lost email, invoices landing in spam, a week of downtime — come from doing the right steps in the wrong order. Here's the sequence that keeps mail flowing, what moves cleanly from Google Workspace, and the traps that catch businesses who do it themselves.
A well-run Microsoft 365 migration is a sequence, not an event: secure the destination tenant first, copy historical data across in staged passes while the old platform keeps working, cut over the domain's MX records in a quiet window, then run both platforms in parallel for two to four weeks before decommissioning anything.
Done in that order, users notice one change — where they log in on Monday morning. Done out of order, you get the horror stories.
We migrate Perth businesses from Google Workspace, legacy hosting and personal accounts onto Microsoft 365 regularly, and the projects that go smoothly all share the same shape. This guide walks through that shape: the order of operations, what migrates automatically and what has to be rebuilt, and where the risk actually concentrates (spoiler: it's a 30-minute DNS window, not the weeks of data copying).
Step one is security, not data
The counterintuitive part of a good migration plan: the first work happens in the destination tenant, before a single email moves. Multi-factor authentication enforced for every account, legacy authentication blocked, admin roles protected, and Conditional Access policies configured if your licensing includes them.
The reason is simple. The moment your company's entire email history lands in Microsoft 365, that tenant becomes the most valuable target you own. Attackers watch for exactly this window — new tenants, default settings, passwords set in a hurry and MFA "coming later". Securing the empty tenant costs a few hours; securing a compromised one costs a great deal more.
This is also the point where the licensing decision gets made, because it changes what security you can turn on. Conditional Access and Intune device management need Business Premium — our Premium vs Standard breakdown covers that decision in detail.
What migrates cleanly — and what doesn't
Migration tooling has matured to the point where the core data moves reliably. The surprises live at the edges:
| Item | How it moves |
|---|---|
| Email, calendars, contacts | Migrates via tooling in staged passes, including folder structure and read status. Calendar resources like meeting rooms are the exception; they're recreated manually in Exchange Online |
| Google Drive files | Migrates to OneDrive (personal drives) and SharePoint (shared drives). Docs, Sheets and Slides convert to Word, Excel and PowerPoint automatically: clean for simple files, worth checking for complex spreadsheets |
| Sharing permissions | Do not migrate. Who-can-see-what must be re-applied on the Microsoft side — plan for this, because it's the most commonly missed step |
| Google Groups | Recreated by hand as distribution lists, Microsoft 365 Groups or shared mailboxes depending on how each group was actually used |
| Google Forms | Do not migrate. Rebuilt in Microsoft Forms, and any links to the old forms updated |
| Mail rules, filters, signatures | Recreated per user or centrally in Exchange Online (a good moment to standardise signatures while you're at it) |
| Deep folder paths | SharePoint and OneDrive cap the full path plus filename at 400 characters. Deeply nested Drive folders with long names need flattening before they'll copy |
The staged copy: why nobody notices the migration happening
The actual data transfer is the least dramatic part of the project, because it's designed to run while everyone keeps working on the old platform:
The three-pass mail migration
How mail moves without a cutover gap
- Pre-stage pass — everything older than about 30 days copies across first. This is the bulk of the data and it can run during business hours, because nobody misses email from last quarter while it's copying.
- Catch-up pass — the recent remainder copies overnight, bringing the new mailboxes to within hours of current.
- Delta pass — after cutover, a final sweep catches anything that arrived on the old platform while DNS was propagating. This pass is why staged migrations don't lose mail.
A pilot group of two or three users moves first and works from Microsoft 365 for a week before everyone else follows. Every migration surprise you can have, you'd rather have with three users than thirty.
Cutover: thirty minutes of DNS, done carefully
The moment of truth is changing your domain's MX records, the DNS entries that tell the world where your email lives. It's scheduled for an evening or weekend, and it only happens once every mailbox is verified, every user can log in, and the pilot group has been living in Microsoft 365 without drama.
The spam-folder trap
The most common self-migration failure isn't lost email — it's the mail authentication records. SPF, DKIM and DMARC tell receiving servers your mail is legitimate. Migrating changes which servers send your mail, so all three must be updated to point at Microsoft: a new SPF record, DKIM signing enabled with its two DNS entries, and DMARC aligned.
Skip this and everything appears to work — until your invoices and quotes quietly start landing in customers' junk folders. Businesses often discover it weeks later, from a client who "never got" something important. Verify all three records the same night as cutover, not later.
Don't turn Google off. Not yet.
The old platform stays alive after cutover, typically 30 days minimum. It costs one more month of licensing and it buys you three things: a safety net if anything didn't copy, a final delta of any stragglers, and time for the things nobody remembered to list in the audit — the invoicing tool that authenticates with Google, the scanner that emails via Gmail SMTP, the one shared calendar someone's bookkeeper relies on.
Decommissioning is its own checklist at the end: export anything residual, cancel the subscription, and strip the old Google records out of DNS. Only after everyone has lived in the new platform for a few weeks without reaching backwards.
Timeline and cost
For a typical Perth business of 5–20 staff: a few days of assessment and tenant build, one to two weeks of background copying, a cutover weekend, and the parallel-running tail. Users experience roughly one hour of change — new login, Outlook and OneDrive set up on their machines, a short walkthrough.
We quote migrations as a fixed scope after a short audit of user count, mailbox sizes, shared drives and third-party integrations — a defined project deserves a defined price, not an open-ended hourly bill. Work outside the fixed scope is charged at $180/hr ex GST, one-hour minimum, then 30-minute increments, with no call-out fee in metro Perth. The full service — including training and post-migration support — is on the Google to Microsoft 365 migration page, and for moves that are more about files and systems than email, see data migration.
Migration Questions, Answered
What businesses ask before making the move.
How long does a Microsoft 365 migration take?
For a typical small business of 5 to 20 staff, plan on two to four weeks end to end: a few days of assessment and tenant setup, one to two weeks of background data migration, a cutover weekend, and a parallel-running period afterwards. The bulk copy runs while everyone keeps working — the only user-visible change happens at cutover.
Will we lose emails during the migration?
Not if it's staged properly. Historical mail copies across before cutover while the old platform still receives everything, the MX change happens in a quiet window, and a final delta pass catches anything that arrived during DNS propagation. The old mailboxes stay alive for weeks afterwards as a safety net.
Do Google Docs and Sheets convert to Word and Excel?
Yes — Docs, Sheets and Slides convert to Office formats automatically during the Drive copy. Simple documents convert cleanly; complex spreadsheets need checking afterwards. Two things don't migrate at all: Google Forms (rebuilt in Microsoft Forms) and sharing permissions (re-applied on the Microsoft side).
Can we keep our email addresses?
Yes. Your addresses belong to your domain, not to Google or Microsoft. The domain is verified in Microsoft 365 before migration, accounts are created with the same addresses, and at cutover the MX records point at Microsoft instead of Google. From the outside, nothing changes.
Can you migrate from personal Gmail or a personal Microsoft account?
Yes. Businesses that grew up on free Gmail or personal Outlook accounts can move that history into a proper business tenant, usually via IMAP migration. The main constraint is message size — IMAP migration caps messages at 35MB by default, raisable to 150MB before the run, which matters because old personal mailboxes are full of oversized attachments.
What does a migration cost?
Migrations are quoted as a fixed scope after a short assessment of users, mailbox sizes, shared drives and integrations. Ad-hoc work around a migration is $180/hr ex GST, one-hour minimum, then 30-minute increments, no call-out fee in metro Perth. Migration tooling licences are passed through at cost.
Related
Where to go next, depending on where you are in the move.
Thinking about making the move?
We'll audit what you're on, tell you what the migration involves for your specific setup, and quote it as a fixed price — in writing, before anything moves.
Support Perth IT Pty Ltd · Perth, Western Australia · $180/hr ex GST, one-hour minimum, then 30-minute increments · No call-out fee in metro Perth. Migration projects quoted as fixed scope after assessment.