Microsoft 365 migration

Moving Microsoft 365 to a new tenant.

A merger or split, a rename, a fresh start on a clean tenant after years of clutter in the old one. Mailboxes, calendars, contacts and files then have to move from one tenant to another. We wrote our own tool for this on Microsoft Graph and run the whole migration, from planning to the domain cutover.

Tenant-to-tenant

Microsoft Graph

Mail · calendars · contacts

OneDrive · SharePoint

PST import

Scope

What M365 Migrator moves

Accounts are paired from a list: old address → new address. Each account is migrated on its own.

Mail

Messages from user mailboxes, mapped to the new accounts.

Calendars

Meetings and events from user calendars.

Contacts

Users' address books.

OneDrive

Files from each person's OneDrive.

SharePoint

Files from SharePoint document libraries.

PST archives

A separate script imports old Outlook archives (.pst) into the mailbox in the new tenant.

Process

How the migration runs

1. 01 Preparation We register an app in both tenants (Microsoft Entra ID) and list the account pairs to move.
2. 02 Test Before any data moves, the script checks permissions and the connection to both tenants.
3. 03 First pass We move everything. Accounts run in parallel, and a failure on one does not stop the rest.
4. 04 Catch-up and cutover The tool remembers what it has already moved. A pass just before the domain cutover picks up only new items, with no duplicates.

Our part

The tool is half the job

A plan and a cutover date agreed with you, so everything works the next morning

Moving the domain to the new tenant and switching the mail records in DNS

Setting up Outlook and OneDrive for users, remotely via BonDesk or on site

A check afterwards: is mail arriving, are files and calendars complete?

To be clear

What the tool does not move

Microsoft Teams chats and channels are not part of the migration. If Teams matters to you, we agree on an approach during planning, before anything starts.

Questions

Frequently asked

Can I use the tool myself?

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Get in touch. We also make the tool available to administrators at other companies, discuss the terms and help with the first run.

Do users lose access to mail during the migration?

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No. Until cutover day everyone keeps working in the old tenant while we copy data in the background. There is only a short break during the domain cutover itself, which is why we schedule it for an evening or weekend.

How long does a migration take?

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It depends on the number of accounts and the amount of data. So we review both tenants first and give you a date afterwards.

Which way does the data travel?

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The script runs on a machine with PowerShell. Data goes from one tenant to the other through Microsoft Graph, with no third-party cloud service in between.

Our mail is not on Microsoft 365. Can you still help?

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The tool works between two Microsoft 365 tenants. Mail from another server can be exported through Outlook into PST archives, which we then import into the new mailboxes with the script.

Planning a tenant move?

Tell us how many accounts there are and what needs to move. We will reply with how we see the process and where to start.

Contact

Let's talk about your IT

The first call is always free. No pitch deck — we ask what is broken and tell you what can be done about it.

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