A Microsoft 365 tenant-to-tenant migration can quickly become complicated when several workloads are involved. Email, OneDrive, SharePoint, Teams, contacts, calendars, and shared mailboxes all have different data structures, so treating the entire migration as one simple file-transfer task can create problems later.

I would begin with a detailed inventory of both tenants. Identify the users, mailboxes, OneDrive accounts, SharePoint sites, Teams, and shared mailboxes that actually need to move. From there, create source-to-destination mappings. This becomes particularly important during mergers or organizational restructuring, where usernames and site structures may change between tenants.

A SysInfo Microsoft Tenant Migration Tool  can make this process easier when multiple workloads have to be handled together. Having mailbox, OneDrive, SharePoint, and Teams options available in one application can reduce the need to coordinate several unrelated migration workflows.

Data filtering is another thing I would test early. Not every mailbox necessarily needs years of historical emails. A date-range filter can be useful for phased migrations or when only recent communications need to be moved. For OneDrive and SharePoint, file-extension and file-size filters can similarly help define the migration scope.

I also think incremental migration is important for projects that cannot be completed in one maintenance window. After an initial transfer, administrators may need to move newly created or modified data. A skip-previously-migrated option can prevent already transferred items from being processed again.

The Office 365 tenant migration tool I reviewed also supports OAuth 2.0 authentication through Microsoft's authentication system. This is useful for environments where MFA is enabled and administrators do not want to rely on storing passwords inside the migration application.

Teams deserves separate testing because its data model differs from ordinary mailboxes and files. Channels, chats, files, and Planner data may need to be validated individually after migration. The product uses Microsoft's Migration API for Teams and Graph API for other supported Microsoft 365 workloads.

Finally, I would not start with the entire organization. A pilot involving a few different users, SharePoint sites, OneDrive accounts, and Teams would provide a much better indication of how the migration will perform.

A tenant to tenant migration tool should therefore be evaluated using real-world test data, mapping requirements, authentication, filtering, incremental transfers, and post-migration reports rather than simply looking at the number of supported workloads.