Email migration is one of those projects that looks simple until you're in the middle of it. Moving mailboxes, calendar data, contacts, and shared folders between platforms without losing anything - and without the business grinding to a halt - requires careful planning. This guide explains what actually happens during an email migration and how to set your Perth business up for a smooth cutover.
Common email migrations we handle
- On-premise Exchange server → Microsoft 365
- Google Workspace (Gmail) → Microsoft 365
- Hosted email (cPanel, Crazy Domains, GoDaddy) → Microsoft 365
- Old Microsoft 365 tenant → new Microsoft 365 tenant (e.g. after a rebrand or acquisition)
- POP3 or IMAP mailboxes → Microsoft 365
Phase 1: Audit and preparation (1–2 weeks before cutover)
Most email migration problems originate in this phase - or rather, from skipping it. Before touching anything, you need to know exactly what you're moving.
Mailbox inventory
List every mailbox: user mailboxes, shared mailboxes, distribution lists, resource mailboxes (meeting rooms), and any functional accounts (info@, accounts@, support@). Migrations fail when something is discovered halfway through that wasn't in scope.
Mailbox size audit
Large mailboxes take longer to migrate and can hit limits. If someone has 80GB of email going back 15 years, their mailbox will take much longer to move than a standard user's. This affects timeline planning significantly.
Clean up first
Encourage staff to archive or delete old emails before the migration starts. Moving 80GB when 60GB of it is 10-year-old newsletters wastes time and storage. It's also a good opportunity to clean up shared mailboxes that no one actively uses.
Calendar and contact data
Calendars and contacts migrate differently depending on the source platform. Check that recurring meetings, shared calendars, and contacts all have a clear migration path - these are frequently the things that cause confusion post-cutover.
DNS and domain verification
Before cutover, the destination platform needs to verify ownership of your domain. This is usually done by adding a TXT record to your DNS. Depending on who manages your DNS and how quickly changes propagate, this can add a day or two to the timeline.
Phase 2: Pre-migration (running in background)
Once setup is complete, the initial data migration runs in the background. This is a “seeding” phase - all historical emails and data are copied to the new platform before any cutover happens. During this time:
- Staff continue using their existing email normally
- No disruption to sending or receiving
- The migration tool syncs incrementally, keeping the new mailboxes up to date
For large mailboxes this can take several days. For a business moving 20 users with typical mailbox sizes, the pre-migration usually completes in 24–48 hours.
Phase 3: Cutover
Cutover is the moment new emails start going to the new platform instead of the old one. It's done by updating the DNS MX records - the records that tell the internet where to deliver email for your domain.
A well-planned cutover:
- Runs a final sync to get all mail sent since the pre-migration started
- Updates the MX records to point to the new platform
- Waits for DNS propagation (typically 15 minutes to 4 hours, but can be up to 48 hours in rare cases)
- Confirms new emails are arriving at the new platform
- Reconfigures Outlook and mobile devices to connect to the new server
During DNS propagation, some emails may still route to the old system - which is why keeping the old system active for 24–48 hours post-cutover matters. Those emails get caught by the final sync. Once things have settled, run our free DNS Health Checker to confirm the old MX records and any other leftover settings have actually been cleaned up, not just working around a cached record.
Common problems (and how to avoid them)
Staff devices not reconfigured
After cutover, Outlook, Apple Mail, and mobile email apps need to be reconfigured to connect to the new server. If this isn't planned, staff find themselves unable to send email from their devices even though the migration "worked". For larger teams this requires hands-on time - budget for it.
Shared mailboxes missed
The info@ or accounts@ mailbox is often used by multiple staff from their own Outlook. If these shared mailboxes aren't migrated and reconfigured in everyone's Outlook, you'll get calls from staff who can't access them the morning after cutover.
Two-factor authentication catching people out
Moving to Microsoft 365 usually involves enabling MFA. Staff who didn't set up the Authenticator app before cutover can find themselves locked out on the first morning. Pre-enrol MFA for all users before cutover day.
Email signatures broken
Centralised email signatures often break when the platform changes. If your business uses a signature management tool or a server-side signature injector, test this specifically before cutover.
Third-party integrations
Any system that sends or receives email using SMTP credentials - accounting software, booking systems, CRMs, printers - will need its credentials updated to match the new platform. These are easy to miss and often only noticed when the system stops sending confirmation emails.
Timeline summary
| Phase | Typical duration |
|---|---|
| Audit and preparation | 1–2 weeks |
| Pre-migration (data seeding) | 1–5 days depending on size |
| Cutover window | Planned for Friday evening or weekend |
| Post-cutover monitoring | 24–48 hours |
| Device reconfiguration | Scheduled before or immediately after cutover |
For most Perth businesses with 5–30 users, the total project runs 2–4 weeks from kickoff to completed.
Frequently Asked Questions
Will we lose emails during a migration?
Not if it's done correctly. A well-planned migration copies all historical emails before cutover, runs both systems in parallel during the transition, and only redirects the DNS MX records once everything is confirmed working. You shouldn't lose any emails.
How long does an email migration take?
The pre-migration setup typically takes 1-2 weeks. The actual data migration can run in the background over several days for large mailboxes. The cutover itself, the DNS switch that redirects new emails to the new system, takes minutes, but the total project is usually 2-4 weeks from start to finish.
What is the best time to do an email migration?
Plan the DNS cutover for a Friday evening or weekend if possible. This gives the migration team time to monitor the transition and resolve any issues before the business returns on Monday. Avoid migrating during your busiest season or around key deadlines.
Will staff need to reconfigure anything on their own devices?
Usually yes, at least a little. Outlook and mobile mail apps typically need to reconnect to the new server after cutover, and this is easy to miss if it isn't planned for ahead of time. A well-run migration schedules this reconfiguration as part of the project rather than leaving staff to figure it out on the morning of the switch.
Planning an email migration in Perth?
We handle email migrations to Microsoft 365 for Perth businesses - from audit through to post-cutover support. No lost emails, no nasty surprises.
Get a migration quote →For related reading, see our Google Workspace to Microsoft 365 migration guide and Email Security for Perth Businesses.