Office 365 Tenant to Tenant Coexistence Setup Guide


Office 365 Tenant to Tenant Coexistence provides coexistence functionality for O365 to O365 migrations. When performing an O365 migration and cutover is planned for a later date, migrations are done in batches. These types of migrations generally require coexistence so that the users on the source and destination can seamlessly communicate. This feature enables migrated users to be able to see the non-migrated users free/busy status and their contact details.  

Note: Migration can be completed in batches, but all the users need to be in the same project. Once a project is set up, users can only be added or removed from the source environment, then use the Rediscover Items button in MigrationWiz to sync those changes. Users cannot be manually added or removed from the migration project.

Important: Office 365 Tenant to Tenant migrations with Coexistence only support migration scenarios where the domain name is changing between the source and destination.  Migrating and keeping the same domain name is not supported at this time.

Important: Azure Active Directory Connect (ADFS, AADConnect, AADSync, ADSync, etc.) cannot be used to do anything with the destination user accounts until after the migration project is fully completed.


  • User Migration Bundle licenses are required for this migration.
  • Only specific Office 365 licenses are supported for this migration. The supported types are listed in the Migration Setup drop-down menu.
    • Only one Office 365 license type can be used per project.
    • The Office 365 license types cannot be changed once the project has been set up.
  • The migration can be completed in batches; however, all the users need to be in the same project.
  • Once a project is set up, you can use the Rediscover Items option in the Manage Tenant to Tenant menu to add/remove users from the project.
    Note: The users must be removed or added to the Source environment before the Rediscover is used.
  • Cloud accounts are created on the destination.
    Note: User passwords will be created as part of the DeploymentPro Profile Configuration.
  • Azure Active Directory Connect cannot be used to do anything with the destination user accounts until after the migration project is fully completed.

Best Practices

  • One the Tenant to Tenant Coexistence option is selected and the migration is saved, the coexistence option cannot be removed. It is recommended to make sure that the scope and time frame of the migration is known ahead of time.
  • A Global Administrator account is absolutely required for both the source and destination endpoints. If one is not available to be used, then this migration type cannot be used.
  • All users on the source will be discovered to create mail-enabled contacts for those items on the destination. This migration type, therefore, is unsuitable for part divestitures from the source tenant. The mail-enabled contacts will be converted into cloud-only user mailboces. Synchronization with on-premises objects with AADC cannot be performed until after the migration.
  • Only a single-target domain is supported.

Setting up the Office 365 Tenant to Tenant Coexistence

  1. Launch MigrationWiz and create a Mailbox project
  2. Set up the Source and Destination endpoints as Office 365. 
  3. Enable Tenant to Tenant Coexistence by selecting the checkbox during the initial project creation.Enable.png
  4. Configure the Tenant to Tenant options.
    • Configure Domain Addresses: Enter the primary Source and Destination vanity domain names.  
      Note: The Source domain is optional and can be left blank. This will enable coexistence for all domains on the Source.
    • Setting Global Administrator Credentials: A Global Administrator account is required on both the Source and Destination endpoints. 
      Important: The destination tenant Administrator account needs to be able to access MSOnline, so the account must use the domain to ensure the correct access levels.
    • Choose Office 365 License: Select the Office 365 License type to be used on the Destination.  When the mail enabled contact is converted to a user account with a mailbox, this is the license that will be applied.
    • Migrate Distribution List and Groups: Select the groups that are to be included as part of this migration.  Changes to the Distribution Lists and Groups can be synced during the project.
  5. Click Save and Go to Summary.
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