Microsoft 365 Migration in 2026: How to Move Your Business Without the Headaches
Moving a business to Microsoft 365 can deliver much more than a new email platform.
Done properly, a Microsoft 365 migration can improve collaboration, remote working, identity security, device management, file sharing and business resilience.
Done badly, it can create missing email, broken permissions, duplicated files, frustrated employees and security problems that follow the organisation for years.
That is why a Microsoft 365 migration in 2026 should not be treated as:
“Move the mailboxes on Friday night and hope everything works on Monday.”
It should be treated as a planned technology and security project.
Microsoft itself provides several migration paths depending on where an organisation is starting from, including Exchange migrations, IMAP migrations, Google Workspace migrations, hybrid Exchange deployments and specialist tools for moving SharePoint, OneDrive and file-server data.
Here is what businesses should consider before making the move.
What Is a Microsoft 365 Migration?
A Microsoft 365 migration means moving some or all of your existing business services into Microsoft's cloud platform.
That might include:
Email and calendars into Exchange Online
Files into SharePoint and OneDrive
Teams collaboration
User identities into Microsoft Entra ID
Device management through Microsoft Intune
Security controls around Microsoft 365
Legacy file-server information
Data from Google Workspace
Data from another Microsoft 365 tenant
Not every migration includes every workload.
A five-person company moving email from an old IMAP provider has a very different project from a 200-user business moving Exchange, file servers, SharePoint and multiple domains.
The first step is therefore understanding what actually needs to move.
1. Assess the Existing Environment Before Touching Anything
A successful migration begins with discovery.
Before moving data, identify:
How many users are there?
How large are the mailboxes?
Which shared mailboxes exist?
Which distribution lists and groups are used?
Where are company files currently stored?
Are there PST archives?
Which applications send email?
Which domains are involved?
Which users have administrator access?
Are there legacy applications depending on the current environment?
This stage is easy to underestimate.
For example, an organisation may think it has 40 mailboxes but later discover several shared accounts, scanners sending through the old SMTP service and an application that depends on the current mail server.
Finding these things before migration is far better than discovering them after the old service has been switched off.
2. Choose the Right Migration Method
There isn't one universal Microsoft 365 migration method.
Microsoft supports several approaches depending on the source environment. Exchange organisations may use cutover, staged or hybrid approaches, while IMAP systems use a different migration process. Google Workspace also has specific migration tooling and procedures.
Larger organisations running Exchange Server may choose a hybrid deployment as an intermediate step.
Microsoft describes Exchange hybrid as providing a combined experience between on-premises Exchange and Exchange Online and specifically notes that hybrid can be used as a step towards moving completely into Exchange Online.
The right approach depends on factors such as:
Number of users
Source platform
Amount of data
Required downtime
Business-critical applications
Identity configuration
Compliance requirements
Whether coexistence is required
Don't select a migration method simply because it sounds easiest.
Choose the one that gives the business the lowest practical risk.
3. Plan the Identity Side Before the Email Side
One of the biggest changes in modern Microsoft 365 is that identity is now central to security.
A migration therefore needs to consider Microsoft Entra ID from the beginning.
That includes:
User accounts.
Administrator accounts.
MFA.
Authentication methods.
Conditional Access.
Security groups.
Device access.
Microsoft describes Conditional Access as its Zero Trust policy engine, using identity and device signals to decide whether and under what conditions access should be allowed.
That makes post-migration security considerably more sophisticated than simply creating Microsoft 365 passwords.
For sensitive accounts, organisations can also require phishing-resistant authentication through Conditional Access authentication strengths. Microsoft specifically documents policies requiring phishing-resistant MFA for administrator roles.
A migration is therefore a perfect opportunity to improve identity security rather than carrying old authentication practices into a brand-new tenant.
4. Move Email Carefully
Email is usually the part employees notice first.
A good migration should consider:
Mailboxes
Shared mailboxes
Calendars
Contacts
Distribution groups
Delegated access
Mail forwarding
Mail-enabled applications
Mobile devices
Outlook configuration
The migration method affects what moves.
For example, Microsoft notes that a basic IMAP migration transfers email only, not calendars and contacts, so organisations migrating from an IMAP environment need to plan those elements separately.
This is exactly why “we'll just migrate the email” can become more complicated than expected.
5. Don't Forget DNS and Mail Flow
Moving the data is only part of the project.
At some point, email delivery needs to be directed towards Microsoft 365.
That means planning DNS changes including records associated with mail routing and Microsoft 365 services.
The timing matters.
Change mail-flow records too early and messages may start arriving in the new environment before users are ready.
Change them too late and mail may continue travelling to the old system.
A good migration includes:
DNS preparation.
Mail-flow testing.
A defined cutover point.
Post-cutover verification.
This is also a good time to review email authentication such as SPF, DKIM and DMARC rather than simply copying whatever configuration existed before.
6. Treat SharePoint and OneDrive as a Project of Their Own
Moving file data is not the same as moving email.
One of the worst approaches is:
“Take everything on the old file server and dump it into one giant SharePoint folder.”
Microsoft recommends planning SharePoint governance before rollout, including the policies, roles and responsibilities controlling how information is managed.
Before migrating files, decide:
Which information belongs in SharePoint?
Which belongs in an individual's OneDrive?
Which data is obsolete?
Which permissions need changing?
What should be archived?
Which departments need separate sites or libraries?
Microsoft provides the SharePoint Migration Tool for moving content from on-premises SharePoint and file systems into Microsoft 365, and its current 2026 migration guidance specifically recommends assessing and remediating content before moving it.
A migration is a great opportunity to clean up years of forgotten data.
There is little value in spending time and money moving 15 years of duplicated rubbish into a modern cloud platform.
7. Test Before the Main Cutover
Never assume the migration will behave exactly as expected.
Test first.
A pilot group can reveal:
Mailbox problems
Outlook issues
Permission mistakes
Missing calendar data
Mobile-device problems
Application dependencies
Authentication difficulties
Unexpected user behaviour
Choose pilot users who represent different parts of the organisation.
For example:
A standard office employee.
A manager.
A mobile worker.
Someone using shared mailboxes.
Someone using specialist applications.
Finding a problem affecting three test users is inconvenient.
Finding it affecting 150 employees at 8:55 on Monday morning is considerably less enjoyable.
8. Plan the Cutover Around the Business
A migration should fit the organisation rather than the organisation fitting the migration.
For many SMEs, major cutover work can be scheduled outside the busiest working period.
But the objective should not simply be:
“Do everything overnight.”
Larger migrations may be staged in batches, and Microsoft supports migration batches for Exchange Online scenarios.
The correct approach depends on the size and complexity of the environment.
A good cutover plan should define:
When migration begins.
Who is affected.
When DNS changes occur.
How users are informed.
Who validates the results.
What happens if something fails.
That last one matters.
Every migration plan should include a rollback or contingency strategy.
9. Secure Microsoft 365 After the Migration
The migration is not complete when Outlook starts sending email.
Security configuration needs reviewing.
That can include:
MFA
Passkeys or FIDO2 where appropriate
Conditional Access
Administrator-role protection
Microsoft Defender
External sharing
Mail forwarding
Audit configuration
Device access
Security alerts
Backup requirements
Microsoft continues to expand phishing-resistant authentication in Entra ID, including passkey deployment and authentication-strength policies.
The key principle is:
Do not migrate old security weaknesses into a new cloud environment.
If every employee previously had excessive access or weak authentication, simply reproducing that configuration inside Microsoft 365 misses a major opportunity.
10. Think About Devices Too
Microsoft 365 migrations increasingly overlap with endpoint management.
If employees access company information from laptops, smartphones and tablets, consider how those devices should be controlled.
Depending on licensing and requirements, Microsoft Intune can be used to manage company devices and support access policies alongside Microsoft Entra ID.
For some businesses, the Microsoft 365 project therefore becomes a broader modernisation exercise:
Move email.
Move files.
Secure identities.
Manage devices.
Improve remote working.
That creates significantly more value than merely swapping one mail server for another.
11. Train Employees Before Monday Morning
Even a technically perfect migration can feel like a disaster if employees don't understand what changed.
Tell users:
When the migration is happening.
Whether Outlook will look different.
Whether they need to sign in again.
How MFA works.
Where shared files now live.
How to use OneDrive and SharePoint correctly.
Who to contact if something isn't working.
Don't send a 47-page PDF titled:
“Microsoft 365 Migration User Guide FINAL v9.”
Most employees won't read it.
Short, practical instructions are usually much more effective.
12. Verify Everything Afterwards
A post-migration review should confirm more than email delivery.
Check:
Internal and external mail flow.
Shared mailboxes.
Calendars.
Mobile devices.
Applications sending email.
File permissions.
SharePoint access.
OneDrive synchronisation.
Security policies.
Administrator accounts.
Backup arrangements.
You should also identify any remaining dependencies on the old environment before decommissioning it.
Turning off the old server too quickly is an excellent way to discover that a forgotten application still depends on it.
What About Tenant-to-Tenant Microsoft 365 Migrations?
Not every project involves moving from an old mail server.
Mergers, acquisitions, restructures and divestments increasingly require data to move from one Microsoft 365 tenant to another.
Microsoft has continued expanding native cross-tenant migration capabilities. In May 2026, Microsoft documented cross-tenant OneDrive and SharePoint migration capabilities, while its migration orchestrator supports tenant-to-tenant scenarios across Microsoft 365.
These projects require additional planning around:
Identity mapping.
Domains.
Permissions.
OneDrive.
SharePoint.
Mail.
Teams.
User communication.
They can be significantly more complex than moving from a conventional mail provider.
Microsoft 365 Migration Is Also a Security Project
This is perhaps the biggest difference between a 2026 migration and the way many businesses thought about Office 365 migrations years ago.
A Microsoft 365 tenant is not simply an email server living somewhere else.
It can become the central identity, collaboration and security platform for the business.
That means migration decisions affect:
Who can access information.
Which devices can connect.
How users authenticate.
How administrators are protected.
How documents are shared.
How security incidents are detected.
The migration team therefore needs to understand more than mailbox copying.
They need to understand the environment the business is moving into.
Planning a Microsoft 365 Migration?
Hamilton Group can help businesses plan and carry out migrations into Microsoft 365 while minimising disruption to employees.
We can help with Exchange Online, Microsoft 365 email migrations, SharePoint, OneDrive, Microsoft Entra ID, Microsoft Intune, Microsoft Defender, Conditional Access, MFA, passkeys, DNS changes and post-migration security hardening.
Whether you are moving from an old mail provider, on-premises Exchange, Google Workspace or another Microsoft 365 tenant, the objective should be the same:
Move the data safely, keep the business working and leave the new environment better secured and easier to manage than the one it replaced.
And when your employees need IT support, our aim is to make first contact within 15 minutes.
Call Hamilton Group on 0330 043 0069 or visit hgmssp.com to speak with one of our Microsoft 365 and IT experts.