How do you handle identity during Microsoft 365 tenant-to-tenant migrations?

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1

Identity is usually the hardest part of a Microsoft 365 tenant-to-tenant migration — more complex than moving mailboxes or files.

From what we’ve seen, successful migrations focus on identity planning first, not last.

Key identity challenges during tenant migrations

  • Mapping users between source and target tenants

  • Preserving UPNs, email aliases, and groups

  • Avoiding SSO breakage for apps relying on OAuth / SAML

  • Managing hybrid or federated identities

  • Ensuring users don’t lose access on Day-1

What works best in real projects

  1. Pre-migration identity assessment
    Audit users, domains, groups, and authentication methods before moving any data.

  2. Clear identity mapping strategy
    Decide early how users will be matched or recreated in the target tenant (same UPN vs new domain).

  3. Parallel identity + workload migration
    Identity should move alongside mailboxes, OneDrive, Teams, and SharePoint — not as a separate task.

  4. Use a dedicated tenant-to-tenant migration platform
    Tools built specifically for cross-tenant migrations reduce manual identity errors and help keep permissions, access, and user context intact.

In our experience, platforms like CloudBik help by orchestrating tenant-to-tenant migrations in a structured way — covering workloads while aligning user identities and access across tenants. This is especially helpful in M&A, tenant consolidation, divestiture, or rebranding scenarios.

Curious to hear from others:

  • How do you prevent identity or SSO issues during tenant migrations?

  • Any lessons learned or best practices you’d recommend?

2

We’re planning a Microsoft 365 migration after a business restructuring, and one area I’m still trying to fully understand is identity management during a tenant-to-tenant (T2T) migration. Moving data seems straightforward enough, but mapping users correctly between the source and destination tenants feels like the most critical step.

I’ve been evaluating the MacSonik Office 365 Tenant-to-Tenant Migration tool because it appears to focus on enterprise migrations while keeping security and accuracy intact. From what I’ve learned, it uses OAuth 2.0 authentication along with the Microsoft Graph API, so authentication stays within Microsoft’s supported framework instead of relying on legacy methods. That gives me more confidence from both a security and compliance perspective.

Another feature that looks useful is its mailbox mapping and migration control. Instead of migrating everything blindly, admins can perform selective workload migration, choose specific folders, and even apply date-range filters. For organizations with hundreds or thousands of users, that level of control seems valuable when validating user identities before the final cutover.

Our environment includes Exchange Online mailboxes, shared mailboxes, OneDrive accounts, SharePoint sites, calendars, and contacts. The tool claims to preserve metadata, folder hierarchy, document properties, and mailbox structure throughout the migration, which should help users transition without noticing major changes. It also supports incremental (delta) migration using the Skip Previously Migrated feature, so only new or modified data is copied during subsequent syncs instead of duplicating existing content.

Another thing I appreciated is that the software operates entirely on the local machine instead of storing organizational data on external servers. Combined with TLS-encrypted HTTPS connections and enterprise-grade encryption, it seems designed with security in mind. The real-time monitoring dashboard and detailed migration reports would also make it easier to verify that every mapped user and workload has been migrated successfully.

For those who’ve completed a Microsoft 365 tenant-to-tenant migration, how did you manage user identity mapping? Did you rely on manual mailbox mapping, automated matching, or a hybrid approach? Were there any unexpected issues with UPN changes, shared mailboxes, or OneDrive ownership that caused problems after the migration? I’d love to hear what worked best in real-world enterprise environments.