Microsoft 365 to Microsoft 365: the complete playbook

This is the end-to-end guide for moving one Microsoft 365 tenant into another with MigrateX — a merger, a divestiture, a rebrand, a consolidation. It covers what to prepare, what happens at each step, what moves and what doesn't, how the domain changes hands, and what to do the morning after. Read it once before you start; keep it open on cutover evening.

1 · Plan the move

Three decisions shape everything else. Make them before you connect anything.

A useful rule: copy in waves, cut over once. Migrate people over days or weeks while the source stays live; move the domain and mail routing on one evening when everything is already in the target.

A realistic timeline (250 people)

2 · Prepare both tenants

In the target tenant

• Create the accounts. A person can only land on an account that exists. Same alias as the source where possible (aisha.rahman@), so auto-match pairs them without help.
• Assign licenses that include Exchange Online (and OneDrive/SharePoint if in scope) and wait for the mailboxes to be provisioned — usually minutes, sometimes an hour.
• If the domain moves, the target needs a fallback domain (its .onmicrosoft.com or another verified domain) that accounts can hold until cutover.
• Have a Global Administrator ready to consent.

In the source tenant

• A Global Administrator for consent; MigrateX also needs the Exchange Administrator role granted to its app for shared mailboxes, rights, aliases and distribution lists (the consent screen handles the app; the role is assigned in Entra ID → Roles).
• Turn off concealed names in usage reports (Microsoft 365 admin center → Settings → Org settings → Reports) so mailbox and OneDrive sizes are readable.
• Decide what stays behind: leavers, service accounts, archived sites.

In MigrateX

• Create the project with the route Microsoft 365 → Microsoft 365 and tick the scope: Mailboxes, Shared mailboxes & aliases, OneDrive, SharePoint, Teams, Microsoft 365 Groups.
• Licenses: one per person, half per shared/room/equipment mailbox; groups, sites and Teams are free. See Licenses and billing.

3 · Connect both tenants

1. Connect the sourceOverview → Connect source tenant. Sign in at Microsoft as the source Global Administrator, check the tenant name, accept the permissions.
2. Connect the targetIn a private window, the same for the target tenant. MigrateX refuses to connect the same tenant at both ends.
3. Check the permission countEach tenant node shows "N of N permissions". If some are missing, wait a minute, Re-check, then Grant consent again.

Full detail, including what each permission is for: Connect a Microsoft 365 tenant.

4 · Assess

Assessment → Run assessment. It reads users, mailbox and OneDrive sizes, shared mailboxes, groups, sites and Teams from both tenants, pairs people up and scores readiness. Typical findings on this route and what to do:

5 · Match users

Auto-match pairs by alias, then email alias, then unique display name. Fix the rest by typing a target address or importing a two-column CSV; exclude leavers. Detail: Matching users.

6 · Pilot

Tick five to ten people on Users and press Migrate selected. Choose on purpose: the two largest mailboxes, someone with many shared OneDrive files, someone with a big calendar, one shared mailbox. When the Migration tab shows them in sync, sign in as one of them in the target and check:

• Folder tree, including nested folders and the archive mailbox.
• A few old messages: the sent date is the original, read/unread and flags match.
• A recurring meeting: recurrence and reminders intact, nobody re-invited.
• OneDrive: a shared file shows the same people with the same roles.

If that all looks right, the rest will.

7 · Mailboxes

Doesn't move: Deleted Items and Junk (on purpose), Outlook client-only settings (views, Quick Steps, local signatures in the desktop app), Microsoft 365 Groups' group mailboxes (the group is recreated; its conversations are not).

Time: minutes to an hour for a normal mailbox; a day or more for 50 GB and up. Everything is resumable and never copies the same item twice. Detail: Migrating mailboxes.

8 · OneDrive

OneDrive moves with each person's mailbox migration. Files stream in chunks through memory; created and modified dates are kept; the current version moves. Sharing is re-granted to the matched people with the same role. Sharing links and external people are listed as notes — recreate the ones you still need. OneNote notebooks are listed rather than copied. Detail: Migrating OneDrive and Drive.

9 · Shared mailboxes, aliases & groups

On Shared & groups, press Read again, wait for the people who use them to be matched, then Migrate selected.

10 · SharePoint

On Sites & Teams, sites are provisioned in the target with the same URL alias, title and template; Owners, Members and Visitors are mapped to target accounts; every document library streams like a drive. Custom lists, workflows, unsupported web parts and site pages are listed by name for manual follow-up. Hub associations are not carried.

11 · Teams

A team is created in the target in migration mode, channel history is imported with the original authors and timestamps, then team files are copied. The team is staged: nobody can use it yet, and delta passes keep it current. When you press Make selected teams available, it leaves migration mode and gets its owners and members. Microsoft accepts no more history after that, so make Teams available on cutover evening, after the final delta.

Not covered by the import API and listed instead: private and shared channels, tabs and apps, reactions, 1:1 and group chats, meeting recordings.

12 · Waves & delta passes

• Migrate in waves that suit the business — by department, by site, biggest mailboxes first. People keep working in the source throughout.
• Run Run delta pass nightly (or whenever): only new and changed items move, and passes are free.
• Workers honour Microsoft's throttling across the board; when Exchange asks for a pause, everything pauses and resumes. You don't need to do anything.
• Failures are retried automatically up to five times; the "Items that need a look" list shows the newest reason for anything still failing.

13 · Verify

Migration → Verify everyone lists every source folder, calendar and drive again and checks each item against the target. Missing items are shown by name; Copy missing items queues them. Verify after the full wave and again after the final delta on cutover evening. Detail: Verification and retries.

14 · Cutover evening

The wizard on Cutover walks these steps in order and checks DNS before you flip. Plan two to three hours; most of it is waiting for DNS.

1. Freeze changesAsk people to stop creating new content in the source for the evening. (Anything that slips through is caught by forwarding and the next delta.)
2. Forward mail from the sourceEach migrated mailbox forwards to its target twin, so mail arriving during the switch lands in the right place.
3. Final delta passThe last hours of mail, files and history.
4. VerifyCopy anything missing.
5. Make staged Teams availableThey leave migration mode and get their members.
6. Release the domain from the sourceMigrateX first moves every source user, group and shared mailbox to the source's fallback domain so nobody loses an address, then removes contoso.com from the source tenant.
7. Add and verify the domain in the targetAdd the TXT record MigrateX shows at your DNS provider; press Check. Microsoft can take from minutes to an hour to release a domain — this is the long wait.
8. Claim the addressesPrimary addresses and every alias on contoso.com are applied to the target accounts, shared mailboxes and groups.
9. Point DNS at the targetMX, SPF (include the target's), Autodiscover CNAME, and DKIM if you use it. The wizard shows the records and checks MX for you.
10. Send the notice, sign offThe drafted notice tells people what changed and what to do; the report goes in the change record.

15 · The day after

• Outlook desktop will prompt for sign-in; a new profile is the clean answer for most people (Autodiscover points at the target now). Cached mode rebuilds the local cache — large mailboxes take a while.
• Phones: remove and re-add the account in Outlook mobile.
• OneDrive sync client: sign out, sign in with the target account, re-sync. Local copies of unsynced changes are kept.
• Teams client: sign out and in; staged teams appear once made available.
• Guests: re-invite from the target tenant.
• Retention, DLP, conditional access are tenant policies — configure them in the target; they do not migrate.
• Keep the source tenant, and forwarding, for a month. Run a delta pass if anyone reports something missing, then verify.

16 · Limits and known gaps

Checklist