There are several architecture approaches for mergers, acquisitions, divestitures, and other scenarios that might lead you to migrate an existing Microsoft 365 tenant to a new tenant.
Cross-Tenant Identity Mapping is a feature that can be used during migrations from one Microsoft 365 organization to another (commonly referred to as a cross-tenant migration).
Suppose that two organizations, Fabrikam and Contoso, each have a Microsoft 365 for business tenant and they want to work together on several projects; some of which run for a limited time and some of which are ongoing.
If you are asked to configure shared email domains cross-tenant to support a merger, acquisition, or divestiture, then you might be aware that Microsoft has historically only allowed a domain to be added to one tenant at a time, requiring you to consider a third-party email rewrite service to provide domain sharing.
This article explains how to migrate mailboxes and service settings from one Microsoft 365 or Office 365 organization to another Microsoft 365 or Office 365 organization in a business-merger scenario.
Commonly, during mergers or divestitures, you need the ability to move your users' Exchange Online mailboxes into a new tenant.
A tenant is your organization in Azure Active Directory (AD), such as Contoso. It includes a dedicated Azure AD service instance that Contoso receives when it gets a Microsoft cloud service, such as Microsoft Intune or Microsoft 365.