Migrate all your workloads and Active Directory with one comprehensive Office 365 tenant-to-tenant migration solution. When deploying an email address rewrite solution, you should communicate this to your end-users and support staff to set proper expectations about the user experience. These differences are also visible in a message thread that is forwarded from an internal recipient to an external party. Internal users will see the recipients as the original address, such as, while external users will see the recipients as the rewritten address, such as.

However, this introduces discrepancies when different users view the list of attendees on a calendar appointment or view the recipients of an email message. This is to ensure that when an internal recipient receives an email or meeting invite, they can see accurate availability information when checking Outlook calendars and Teams status for the sender as well as for other recipients. Most email address rewrite solutions only modify messages that are sent to external recipients and do not rewrite messages sent within the same tenant. A good email address rewrite solution will provide options for you to control the rewrite scope, mitigate impacts caused by spoofing messages, and ensure messages are securely transmitted between the tenants and the email address rewrite solution. When you configure an email address rewrite service for your users, it will process calendar invites as well as email messages, and can perform rewrite for the sender along with any message recipients or meeting recipients that are also configured for domain sharing.

These email address rewrite services intercept messages in transit and modify their headers so that the messages appear to have been sent from an email address that is owned by a different tenant. These solutions will require you to provide source-to-target mapping files for the email address translation.Īlternately, if you have purchased a tenant-to-tenant migration tool, it might include domain sharing functionality that utilizes the migration mappings within the tool. There are multiple services that can perform email rewrite on outbound messages, including tools that you may already have deployed in your environment such as Mimecast or Proofpoint, or by using Exchange Edge Transport servers. Email Address Rewrite SolutionsĪ common solution to this challenge is to configure a third-party email address rewrite service that enables partial domain sharing functionality. With this restriction in place, you cannot assign email aliases cross-tenant and you will need to consider alternate methods to address these domain-sharing requests for your Office 365 migration. While Microsoft has acknowledged this need and has plans to provide a native solution for cross-tenant email domain sharing, at the time of writing (November 2022), Microsoft only allows a domain to be added to one tenant at a time. If you are familiar with the Shared SMTP Namespace functionality available with on-Premises Exchange Servers, you might assume that there is similar functionality in Exchange Online. Contoso asks you to set up domain sharing so that email aliases can be assigned to migrated mailboxes in the Contoso tenant.Contoso acquires Fabrikam and wants to ensure that Fabrikam continues to present its unique brand to the outside world, even after migrating Fabrikam’s resources to the Contoso tenant.Contoso asks you to set up domain sharing so that Fabrikam users can send emails from email addresses prior to migrating those users to the Contoso environment.Contoso acquires Fabrikam and wants to present a unified brand to the outside world, ideally on the day they go public with the M&A announcement.Your coexistence needs will usually fall into one of the following two scenarios: If you are supporting the IT integration of a merger, acquisition, or divestiture, you will probably be asked at some point to configure shared email domains across multiple tenants, either to provide pre-migration rebranding or post-migration brand maintenance. The Merger and Acquisition Domain Sharing Challenge Join me at TEC 2022 in Atlanta for more!.Tenant to Tenant Migration Considerations.The Merger and Acquisition Domain Sharing Challenge.

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