Microsoft 365 Migration: A Guide for Small Business

We do Microsoft 365 migrations pretty much every week, and I'll be honest, the ones that go badly are almost always because someone rushed it. I've seen migrations where nobody checked mailbox sizes beforehand and hit the 50GB limit halfway through. I've seen businesses lose a week of calendar data because they didn't test the migration tool properly. And I've seen at least three companies get their MX records wrong and wonder why emails were vanishing into thin air for two days.

So here's how to do it properly, based on everything we've learned from doing this hundreds of times.

Before You Touch Anything

1. Pick the Right Plan

For most UK small businesses, it comes down to two options:

• Microsoft 365 Business Basic (£4.50/user/month) - You get web versions of Office, Exchange email, Teams, SharePoint, and 1TB OneDrive. Good if your team doesn't need the desktop apps.
• Microsoft 365 Business Premium (£18.20/user/month) - Everything above, plus the full desktop apps, Intune for device management, Azure AD P1, and Defender for Business. If you handle any kind of sensitive data, this is the one you want.

I'd recommend Business Premium for most businesses. The security features alone - Conditional Access, device management, Defender - justify the extra cost. You can't bolt that stuff on cheaply later.

2. Know What You're Working With

Before you migrate anything, get a proper picture of what you've got:

• How many mailboxes you have and how big they are (we once found a mailbox with 47GB of attachments, and that's going to cause problems)
• Shared mailboxes, distribution lists, and aliases. People forget about these until something stops working
• Calendar data, contacts, and recurring meetings
• Where files actually live: network drives, local drives, Dropbox, Google Drive, random USB sticks in desk drawers
• What other systems connect to your email: your CRM, accounting software, booking system, anything that sends or receives emails

3. Clean Up Before You Move

Migration is the perfect excuse for a clear-out. Delete mailboxes for staff who left two years ago. Archive emails older than a couple of years. Kill those distribution lists that nobody uses. Every bit of junk data you migrate is time and money wasted. Don't move mess into a new house.

The Actual Migration

4. Set Up Your Microsoft 365 Tenant

Create the account, verify your domain, and get your DNS records right: MX, CNAME, TXT for SPF, DKIM, and DMARC. I can't stress this enough: get DNS right first. We've cleaned up migrations where incorrect SPF records meant half the company's emails were landing in spam for a fortnight. Not fun.

5. Create Users and Assign Licences

Set up each person with the right licence and their primary email address. Set up shared mailboxes. Good news, these don't need licences. Configure your security groups and distribution lists.

6. Set Up Security BEFORE You Move Data

This is where people cut corners and live to regret it. Before any data goes across, configure:

• Multi-Factor Authentication (MFA) - every single user, no exceptions. Day one.
• Conditional Access - block sign-ins from dodgy locations, require compliant devices.
• Anti-phishing policies - set up Defender for Office 365 properly.
• Data Loss Prevention (DLP) - especially if you handle financial or personal data.

We configure all of this as standard through our security services. I've seen a business get compromised within 48 hours of going live on M365 because they hadn't turned on MFA. Don't be that business.

7. Migrate the Email

How you do this depends on where you're coming from:

• From IMAP (most web hosts): Microsoft's built-in IMAP migration tool in the Exchange admin centre does the job.
• From on-premise Exchange: Hybrid or cutover migration, depending on how many mailboxes you've got.
• From Google Workspace: Microsoft has a dedicated tool that handles email, calendar, and contacts in one go.

If you've got more than 20 mailboxes, do it in batches. Migrate the first batch, test everything thoroughly, then do the rest. Don't try to move 50 mailboxes in one shot on a Friday afternoon. Trust me on that one.

8. Move Files to SharePoint and OneDrive

Shared drives go to SharePoint document libraries. Personal files go to OneDrive. Use the SharePoint Migration Tool if you've got a lot of data. And please, set up proper permissions. Don't just dump everything into one giant shared library where everyone can see everything. That's a GDPR headache waiting to happen.

9. Get Teams Right

Set up channels that actually reflect how your business works: departments, projects, clients. Sort out your external access policies. And here's the thing nobody tells you: you need to train people on when to use Teams chat versus channels versus email. If you don't, they'll use Teams like WhatsApp, email like they always have, and you'll end up with information scattered across three places instead of one.

10. Cut Over and Switch Off the Old System

Once everything's migrated and tested, update your MX records to point at Microsoft 365. Give it 24-48 hours for DNS to propagate. Watch for bounced emails like a hawk. Once you're confident, switch off the old system. Don't leave it running "just in case" for six months. That's how you end up paying for two systems.

Mistakes We See All the Time

• Not setting up MFA: One compromised account can give an attacker access to your entire tenant. This is non-negotiable.
• Skipping the parallel run: Run both systems for at least a week. Send test emails to and from external addresses. Check calendars. Check shared mailboxes. Check everything.
• Forgetting third-party integrations: Your CRM, booking system, and accounting software probably send email. They'll need new SMTP settings. Work this out before cutover, not after.
• Assuming Microsoft backs up your data: They don't. Not properly, not long-term. Get a third-party backup like Veeam for Microsoft 365. This catches people out constantly.
• Not training the team: If nobody shows your staff how to actually use Teams and SharePoint, they'll go right back to emailing spreadsheets around. Budget for training. It's not optional.

Want Us to Handle It?

We do Microsoft 365 migrations for UK businesses every week, from 5-person startups to 200-seat organisations. We handle the planning, security configuration, data migration, DNS cutover, and staff training. Then our managed IT services keep everything running, monitored, and optimised going forward.

Get in touch for a free migration scoping call. We'll tell you exactly what's involved and what it'll cost. No surprises.