Merger and separation of Microsoft 365 tenants

Merging tenants, separating perimeters or migrating identities and data are now strategic operations, with high stakes in terms of security, service continuity and governance. This use case illustrates how IT Systèmes supported a customer in the complete merger of two M365 tenants.

Contents :

Example H2

Why companies should merge or separate their Microsoft 365 tenants

In a context of continuous transformation: acquisitions, disposals, restructuring, creation of new entities, or migration from Google Workspace. Our customers regularly need to evolve their Microsoft 365 environment.
These operations involve merging tenants, separating perimeters, transferring identities and data, and maintaining service continuity.
These are highly sensitive processes: they directly affect corporate communications, collaboration, security and compliance.

Customer challenge: achieve tenant-to-tenant migration without service interruption

As part of an acquisition, our client needed to integrate an external entity's Microsoft 365 environment into its main tenant.
The main challenges were:

Merging identities and harmonizing access
Migrate data and services (Exchange, SharePoint, OneDrive, Teams)
Manage domain, alias and permission conflicts
Ensure total continuity of service for users

Our approach: a structured methodology to secure the merger of M365 tenants

Analysis and scoping: audit of source and target environments

Complete evaluation of source and target environments
Inventory of users, licenses, data and application integrations
Dependency analysis (authentication, MFA, SSO, third-party applications)
Risk identification: conflicts, coexistence, safety, compliance

Architecture design: Microsoft 365 tenant-to-tenant merger strategy

Define tenant merger strategy: identities, domains, governance
Migration plan structured by workload (Exchange, SharePoint, Teams)
Implementation of safety and compliance rules adapted to the project
Preparation of switchover scenarios with management of transitional phases

Technical implementation: preparation, configuration and Cross-Tenant migration tools

Environment configuration (DNS, authentication, authorizations)
Implementation of Microsoft Cross-Tenant migration tools (Exchange, Teams, SharePoint), complemented by PowerShell and Graph APIs
Account harmonization : UPN, aliases, groups, permissions
Preparing scripts and pilot environments

Migration & support: transferring identities, data and services

Batch migrations: users, data, sites and teams
Conflict management and systematic access validation
Increased support for IT teams and communication with users
Adjustments, optimizations and skills transfer

The results: a transparent, secure and governed M365 merger

Gradual, transparent merging of the holding company
Full integration of the acquired entity into the main M365 environment
Secure access and data throughout the migration process
Unified governance and consolidated environment, facilitating future management
Guaranteed service continuity for all users

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