Combine Office 365 tenants after a merger or acquisition

When organizations combine infrastructures because of a merger or acquisition, Exchange admins have their work cut out for them. One task might be to merge Office 365 tenants.

As more organizations move to Office 365, the chance that two merging organizations will both have Office 365 greatly increases. After an acquisition, companies often want to consolidate infrastructure and reduce duplication while using a single vendor.

In a traditional on-premises scenario, this typically involves a cross-forest Active Directory migration to the acquiring company forest. If it’s a merger, this might require a completely fresh infrastructure. For Exchange, admins would typically upgrade the mailboxes’ final home where necessary and build it out to ensure it can handle new mailboxes.

The traditional cross-forest migration for Active Directory doesn’t necessarily change with Office 365 tenants — but the Exchange cross-forest migration challenge changes. Rather than solve the problem of redesigning the infrastructure with reasonably straightforward moves, the challenge becomes the migration strategy itself. This is because it isn’t possible to directly migrate mailboxes from one tenant to another.

In this four part series on SearchExchange I explore how to prepare for, then achieve this using a Hybrid Server or MigrationWiz:

Part One
Part Two
Part Three
Part Four