Planning a smooth Microsoft 365 tenant-to-tenant migration

Microsoft 365 tenant-to-tenant migrations are complex projects that require careful planning to avoid disruption, data loss and identity issues. Whether driven by mergers, acquisitions or organisational restructuring, moving between tenants impacts users, email, files, devices and security controls.

A successful migration starts long before the first mailbox or file is moved. Clear preparation and validation at each stage are essential to ensuring a smooth transition for both IT teams and end users.

Assessing the current and target environments

The first step in any tenant-to-tenant migration is understanding both the source and target environments. This includes reviewing user accounts, domains, licences, mail flow, security policies and identity configurations such as Entra ID and Conditional Access.

Identifying differences early helps avoid unexpected issues later in the migration and allows teams to design a realistic migration plan.

Preparing users, data and identities

Preparation is critical to minimising disruption. User communication, licensing alignment and identity planning should be completed before migration begins. Decisions around identity matching, domain moves and coexistence must be clearly defined.

Mailboxes, SharePoint sites, OneDrive data and Teams configurations should be assessed to ensure they are ready to move and free from legacy issues.

Executing the migration in phases

Most tenant-to-tenant migrations are best delivered in phases rather than as a single cutover. Staged migrations reduce risk, allow issues to be resolved early and minimise the impact on users.

Testing pilot groups before full rollout helps validate tools, processes and end-user experience.

Post-migration validation and optimisation

Once migration is complete, validation is essential. This includes confirming data integrity, access permissions, mail flow, Teams functionality and security policies.

Post-migration is also an opportunity to optimise the environment, remove legacy configurations and ensure users are fully adopted into the new tenant.

Ensuring a smooth transition for users

A well-planned tenant-to-tenant migration balances technical execution with user experience. Clear communication, structured support and thorough validation ensure users can continue working with minimal disruption.

With the right planning and approach, organisations can migrate confidently while improving their Microsoft 365 environment for the future.