Microsoft 365 Email Migration: How to Move Without Losing Mail
Moving a company's email looks simple from the outside and goes wrong very publicly. Whether you're leaving mail bundled with old web hosting, retiring an on-premises Exchange server or moving from another cloud, the difference between a quiet weekend and a week of chaos is almost entirely preparation. Here's what a competent Microsoft 365 migration looks like, so you can judge a plan before you commit.
Start with an audit, not a date
Most migrations that go badly were scoped badly. Before anyone touches a setting you need an honest inventory of the email your business runs on — nearly always more than the staff list.
- Every mailbox and its size. Large, old mailboxes take far longer to copy than people expect, and that shapes your timeline.
- Aliases and shared mailboxes. The info@ and accounts@ addresses three people quietly share are the ones nobody remembers until they stop working.
- Distribution lists and forwarding rules. Silent forwards to personal addresses turn up often and are worth reviewing anyway.
- Anything that sends mail without a person. The office scanner, the website contact form, invoicing software, alarm and alert systems.
- Where mail is read. Outlook, phones, tablets, a browser — and whether any of it is too old to connect to a modern service.
Cutover or staged, and what the choice really means
Broadly there are two approaches. A cutover moves everyone at once: you prepare the new mailboxes, copy the mail across, then switch the whole business over in a single window. It's simpler to reason about and suits smaller teams. A staged move shifts people in batches over days or weeks, which limits the size of any one failure but means the old and new systems must coexist and route mail between themselves in the meantime. Neither is automatically right, and nobody should recommend one before asking how many mailboxes you have and how much downtime you can absorb.
Lower your DNS TTL before you touch anything
Your MX records tell the world where to deliver your mail, and every DNS record carries a TTL — how long other servers may cache the answer before checking again. If it's long, some senders keep posting mail to the old destination for hours after you've changed it. So lower the TTL on your mail records to a few minutes, well in advance, and the old value expires everywhere. Then when you flip the MX record the world follows within minutes rather than the rest of the day. Put it back afterwards.
The failure that actually loses email
If one thing sinks a migration, it's changing the MX record before the mailboxes are ready. Mail goes where MX says it goes. Point it at Microsoft 365 before the accounts exist and are licensed, and inbound messages are rejected or land in empty mailboxes nobody is watching, while the old system quietly stops receiving.
The safe order never changes: create and license the mailboxes, copy the historic mail across, verify it arrived, test sending and receiving, and only then change DNS. The MX change should be the last step and the least dramatic one.
Keep the old mail reachable
Don't cancel the old service the day you switch. Leave it running a while so late messages have somewhere to land and anyone who finds a gap can look. Export archives before the account closes, not after: once a hosting mailbox is deleted it is usually gone for good.
Test the boring things first
Everyone tests emailing a colleague. Fewer test the scanner in the corner, the booking form on the website, the accounts package that emails invoices, or whether mail from your domain still passes SPF, DKIM and DMARC checks afterwards. Those fail silently, so customers stop hearing from you without anyone noticing. Work through your audit list and confirm each one.
Plan the human side too
The morning after the switch, everyone signs in again — laptop, phone, often a second factor. Get that right rather than improvise: circulate instructions for adding work email to a phone and set up two-factor authentication deliberately. And a cloud provider keeps the service running, not a spare copy of your mail, so your backup strategy should cover the new mailboxes too.
We can plan the move and run it with you
We run Microsoft 365 migrations for businesses across Edinburgh and the Lothians, from Livingston to Musselburgh — the audit, the mailboxes, the copy, the DNS change and the morning after. We also design and host business websites, run email-only hosting, and look after WordPress sites, so your site, your contact form and your MX record stay with one team instead of three. Our business IT support and managed IT services hold the rest steady while you change something this central, with a clear quote before any work.