Microsoft releases preview of cross-tenant domain sharing for Exchange Online (2023)

Hint: The step-by-step planA new one has been updated for this functionplanned release datedated December 2023. The original article saida previously announced date is November 2022.

Table of contents

Microsoft is trying to solve the M&A domain sharing challenge

If you're asked to configure cross-tenant common email domains to support a merger, acquisition, or divestiture, you may know that Microsoft has historically only allowed one domain to be added to one tenant at a time, so you can create a third get partyEmail Rewriting Serviceto provide domain sharing.

Fortunately, Microsoft recognized the need for a native solution and released cross-tenant domain sharing functionality to select customers for private preview(Microsoft-Roadmap-Element 67161). Once this feature is released to the public, which is currently planned for December 2023, you will have a native domain sharing option similar to theShared SMTP namespace functionalityavailable withexchange on siteServer.

Native cross-tenant domain sharing for Exchange Online

Microsoft has shared initial details about this solution with the publicexpected architectureand some of the configuration and management tasks you need to perform when using the native cross-tenant domain sharing feature. As long as Microsoft doesn't make any major changes prior to release, you can follow the steps in the example below to enable cross-tenant domain sharing for a single SMTP domain.

The domain is authoritative in the tenant where you perform primary domain administration. After you have enabled the domain for cross-tenant domain sharing, you can add the domain as an internal relay in additional tenants. Internal relays are a new addition to Exchange Online, but are a familiar concept if you've worked with an on-premises Exchange Server.

Configuration for sharing domains between different tenants

You start by enabling domain sharing for in Tenant A so that you can assign as the primary SMTP address to the mailboxes in Tenant B.

  1. Add as an accepted domain in Tenant A before adding it to other tenants
    • The domain is listed as Type: Authoritative
  1. Configure in Tenant A to enable sharing with Tenant B
    • Once the feature is released, Microsoft will provide full details on this job
  1. Add as an accepted domain in Tenant B
    • The domain is shown as Type: Internal Relays
  1. Configure inbound connectors in each tenant to trust the other tenant
    • Tenant A plug configuration:
      • SenderDomains={;1}
      • TrustedOrganizations={;1}
    • Configuration of client B connection:
      • SenderDomains={;1}
      • TrustedOrganizations={;1}
  1. MX record for points to Tenant A
    • Incoming messages for all addresses are delivered to tenant A and then forwarded to tenant B

Assignment of the primary SMTP address

With the cross-tenant domain sharing architecture, you can now begin mapping email addresses from to mailboxes in Tenant B, which has as an authoritatively accepted domain.

  1. In Tenant B, create a mailbox that has a UPN for a domain owned by Tenant B
  1. Set the primary SMTP in Tenant B's mailbox to a unique address
    • Once the feature is released, Microsoft will provide full details on this job

The user can now send emails from his mailbox in client Bbob@contoso.comalthough this domain is controlled by Tenant A.

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Tenant-to-tenant migration considerations

The release of native cross-tenant domain sharing will provide a much-needed solution for configuring long-term coexistence between multiple tenants and enable consistent branding for users sending and receiving email from different tenants.

However, if you also planTenant-to-tenant migrationsEnabling cross-tenant domain sharing introduces some additional tasks and complexities to consider when performing your email and SMTP domain migrations. Companies that offer third-party migration tools are expected to start incorporating this scenario into their product development to address these new complexities, which are described in more detail below.

Email Migration Considerations

The first important consideration is that you need to change the timing of moving the primary SMTP address from one mailbox in one tenant to another for users who need to keep their existing email identities.

Currently, you must complete this task as part of an SMTP domain migration event because the domain cannot be shared between tenants. However, once you have implemented cross-tenant domain sharing, you must complete this step as part of the email migration event, as the specific primary SMTP address should not be assigned to more than one mailbox at a time. If your email migration tool doesn't have an option to automatically update the primary source and destination SMTP addresses for mailboxes that use shared domains, you must include a task in your migration plan to make these changes yourself.

SMTP domain migration considerations

The second key consideration is the impact that cross-tenant domain sharing can have on migrating SMTP domains from one tenant to another.

Microsoft doesn't allow you to remove a domain from a tenant until you remove the domain from all objects that use it as a UPN or email attribute. If you activate cross-tenant domain sharing, objects in other tenants also use the domain to be moved. It is very important when running your tenant to understand exactly where the common domain is used by all tenantsPlanning for SMTP domain migration.

After you complete a domain migration for a shared domain, you must also reconfigure your tenant domain sharing relationships and possibly reconfigure each object using the shared domain. Once the native cross-tenant domain sharing feature is fully released to the public, you can expect domain migration tools to report on all shared objects and provide guidance for any tasks that cannot be automated and must be performed manually.

Comparison with third-party solutions

As Microsoft continues to release features like domain sharing between different tenants andShared Teams channelsgain access to new options to solve your merger, acquisition and divestment needs. You can also identify ways to reduce reliance on third-party products. Native cross-tenant domain sharing is expected to provide a viable alternative to third-party email rewriting services to meet long-term coexistence needs with ease of setup and management.

For overall tenant-to-tenant migration planning, evaluate and test standalone native capabilities with third-party solutions to see if you can benefit from the job automation and integration that comes with a comprehensive tenant-to-tenant product. Often the answer for your migration project is a balance of both.

Visit Becky at TEC 2022 in Atlanta and learn more!

Tenant-to-tenant migrations are not for the faint of heart. If a migration is imminent or you are in an acquisition-hungry environment, join the tenant migration experts atThe Expert Conference 2022gain an advantage. Join Practical 365 author Becky Cross as she shares the 5 Trends in M&A Cross-Tenant Coexistence. Check out their session summary:

Cross-tenant coexistence services have been static for a long time, consisting primarily of limited GAL synchronization and free/busy services, and possibly domain sharing using address rewrite technologies. However, some new technologies will soon change many of the things that tenant administrators typically do to prepare their Microsoft 365 environments for collaboration during an M&A project. This session will help you prepare for it.


What is an Exchange cross tenant? ›

During mergers or divestitures, you might need the ability to move your users' Exchange Online mailboxes into a new tenant. Cross-tenant mailbox migration allows tenant administrators to use well-known interfaces like Exchange Online PowerShell and MRS to transition users to their new organization.

Does Microsoft support tenant to tenant migration? ›

Most customers work with Microsoft Consulting Services or a Microsoft partner to migrate tenants, including using third-party tools to migrate content. Use the Tenant-to-tenant migration architecture model to understand how to plan for Microsoft 365 tenant-to-tenant migrations and the steps of a migration.

How to migrate mailboxes from one domain to another in Office 365? ›

Migration scheduling
  1. Create master list of user mailboxes you want to migrate.
  2. Create mailbox mapping . CSV file for the third-party migration tool you are using. This mapping file will be used by the migration tool to match the source mailbox with the target tenant mailbox when migration occurs.
Feb 21, 2023

Is Microsoft 365 multi tenant? ›

Multi-tenant management offers a unified form of management that allows Microsoft 365 partner admins the ability to administer all the tenants they manage from a single location. If you're a partner who has a delegated admin role and manages multiple tenants, you can: Move quickly between tenants you manage.

What is tenant coexistence domain? ›

Follow. CloudM Migrate Microsoft 365 tenant to tenant coexistence enables you to migrate end users in batches while maintaining email and calendar connectivity between the domains as data is moved.

How do I move a shared mailbox from one tenant to another? ›

2 answers
  1. Download the PST import tools and key to private Azure Storage location.
  2. Upload or copy the PST files.
  3. Create a PST import mapping file. In the CSV file you will find a couple of columns/parameters: ...
  4. Create a PST import job.
  5. Filter the PST data that will be imported to mailboxes.
  6. Start the PST import job.
Sep 27, 2021

What are the challenges of tenant to tenant migration in Office 365? ›

The biggest challenge associated with migrating Office 365 from one tenant to another is it needs to be a comprehensive migration. Apart from user accounts and data such as files and folders, businesses must also migrate licenses (subscriptions), groups, domains, email system, and Microsoft Teams.

What is Office 365 tenant to tenant migration? ›

A Microsoft 365 tenant-to-tenant migration is the process of migrating workloads from one Microsoft 365 tenancy to another, which can involve the migration of one or many workloads and can include some or all content within a specific workload.

What is the difference between Microsoft tenant and environment? ›

A tenant can include one or more environments; however, an environment is always associated with a single tenant. This example uses two environments for three teams: Sales, Marketing, and Services. Sales and Marketing share an environment so lead information can be easily accessed by both.

How do I migrate users to Exchange Online? ›

In the EAC, go to Office 365 > Recipients > Migration. , and then select Migrate to Exchange Online. On the Select a migration type page, select Remote move migration and then click Next. and select the on-premises users to move to Microsoft 365 or Office 365 and click Add and then click OK.

What is tenant to tenant migration without rebranding? ›

Types of Migrations:

Tenant-to-tenant migration without rebranding: This involves a business unit and brand identity that have been sold together. The identities will migrate to a target tenant and will keep the existing domain as part of the migration.

How do I transfer emails from one domain to another? ›

Migration process
  1. Create destination mailbox at new provider. ...
  2. Migrate emails from your old mailbox into your new mailbox. ...
  3. Transfer domain name (or change MX record) ...
  4. Run delta migration. ...
  5. Set email aliases (optional) ...
  6. Configure your email client applications.

What is the difference between single tenant and multi-tenant in m365? ›

Single-tenant apps are only available in the tenant they were registered in, also known as their home tenant. Multi-tenant apps are available to users in both their home tenant and other tenants.

Is Office 365 single tenant or multi-tenant? ›

While your organization can have multiple Azure AD tenants that you can set up with Azure subscriptions, Microsoft 365 tenants can only use a single Azure AD tenant, the one that was created when you created the tenant.

What is the difference between a domain and a tenant? ›

Each directory has one or more domains. A directory can have many subscriptions associated with it, but only one tenant. A domain (or accepted domain) is a DNS zone for which a tenant has proven ownership (by creating an arbitrarily named DNS record as requested by Microsoft).

How many domains can a tenant have? ›

One fairly common mistake that many organizations can make is to think that because they have multiple DNS domains, they need to have multiple Office 365 tenants. This is NOT true and you can have multiple domains in a single tenant (you can have up to 5000 domains in a single Office 365 tenant, more details here).

How do I enable cross tenant content move feature? ›

Replies (4) 
  1. Download the latest version of SharePoint Online Management Shell.
  2. Confirm that the source OneDrive tenant doesn't have Service encryption with Microsoft Purview Customer Key enabled. ...
  3. Source OneDrive accounts must be set to Read/Write.
Feb 10, 2023

What is my 365 tenant domain name? ›

Find Your Tenant Name Using the Office 365 Portal

Open the Office 365 Admin Center, click Setup and select Domain (direct link) Identify the domain name that has three parts and ends with “”

How many shared mailboxes can a tenant have? ›

Shared mailboxes are free and any user can have complete access to an unlimited number of shared mailboxes, but each shared inbox has a data storage limit of 50GB. You can't log into a shared mailbox directly using Outlook or Outlook Web App (OWA): you must first be granted permissions to the shared mailbox.

How many shared mailboxes per tenant? ›

Based on our knowledge and experience, there is no limitation to creating shared mailbox in the Office 365. and there is no related limitations about shared mailbox numbers.

Can a shared mailbox have full access to another shared mailbox? ›

More than one person can have “full access” to a Shared Mailbox.

What are the common failures when migrating to cloud computing? ›

Trying to execute a migration without an exhaustive plan of action creates a cloud migration risk in itself; making things up as you go along is not conducive to executing a successful tech project. One of the most common causes behind cloud migration failure is a lack of planning.

Can you merge Microsoft tenants? ›

manually merging Office 365 tenants: Which approach should you choose? As there's no native Microsoft solution to move data between tenants, you can either migrate tenants manually or with the use of a dedicated migration tool that will automate much of the work for you.

How do I forward my Office 365 email to another tenant? ›

Sign in to Office 365. Click on the admin app tile. On the Active users page, choose the user who's email you want to forward. On the Email forwarding page, select Forward all email sent to this mailbox toggle, enter the forwarding address, and choose whether you want to keep a copy of forwarded emails.

What type of migration should you use to move to Microsoft 365? ›

Use cutover migration if you plan to move your entire email organization to Microsoft 365 or Office 365 and manage user accounts in Microsoft 365 or Office 365. You can migrate a maximum of 2,000 mailboxes from your on-premises Exchange organization to Microsoft 365 or Office 365 using a cutover migration.

What happens when a mailbox is migrated to o365? ›

Impact of migration to users

Users must create new Outlook profiles: After the mailboxes are migrated and the on-premises accounts are converted to mail-enabled accounts, the users must create a new Microsoft 365 or Office 365 profile in Outlook, and then Outlook automatically connects to Microsoft 365 or Office 365.

What are the benefits of migrating to Office 365? ›

Migrating to Office 365 also provides you with other security features including:
  • Up to date antivirus signatures.
  • Email protection from malware with anti-spam filtering and antivirus software.
  • Microsoft Trustworthy Computing security measures.
Oct 25, 2022

Is Azure single or multi tenant? ›

Azure is itself a multitenant service, and some of our guidance is based on our experience with running large multitenant solutions. However, the focus of this series is on helping you build your own multitenant services, while harnessing the power of the Azure platform.

Is Azure a tenant? ›

An Azure AD tenant is a reserved Azure AD service instance that an organization receives and owns once it signs up for a Microsoft cloud service such as Azure, Microsoft Intune, or Microsoft 365. Each tenant represents an organization, and is distinct and separate from other Azure AD tenants.

What is the benefit of deploying Microsoft 365 and Dynamics 365 in the same tenant? ›

Manage your company's conversations, files, and tools in one collaborative workspace using Microsoft Teams. Integrating Dynamics 365 with Microsoft Teams enables users to easily work with Common Data Service customer information and share files directly from the application.

What is the server name for Exchange Online? ›

The full URL of the Exchange Server address is

What are the different types of migration? ›

internal migration: moving within a state, country, or continent. external migration: moving to a different state, country, or continent. emigration: leaving one country to move to another. immigration: moving into a new country.

Do I assign Exchange Online license before or after migration? ›

You can pre-assign Exchange Online licenses to users with on-premises mailboxes any time before you migrate them. You'll get a warning message that the user hasn't been migrated yet when you do so.

Can I swap tenants? ›

Ask your landlord for permission

You must get permission and follow the proper process. The tenant you are swapping with must also get permission from their landlord.

How do I switch to another tenant? ›

How to Change your Azure Directory Tenant
  1. Sign in and select the subscription you want to use from the Subscriptions page in Azure portal.
  2. Select “Change Directory”
  3. A box will surface to choose the new directory.
  4. Select “Change” Note. ...
  5. Select “Switch Directories” on the subscription page to access the new directory.
Nov 19, 2021

How to migrate OneDrive from one Office 365 tenant to another? ›

How does it work?
  1. Step 1: Connect to the source and the target tenants.
  2. Step 2: Establish trust between the source and the target tenant.
  3. Step 3: Verify trust has been established.
  4. Step 4: Pre-create users and groups.
  5. Step 5: Prepare identity mapping.
  6. Step 6: Start a Cross-tenant OneDrive migration.
Feb 16, 2023

Can I have two email services for one domain? ›

As such, you cannot register a domain directly with multiple email services at once.

What happens to email when you transfer domain? ›

After the domain transfer, create an email address for your domain with your new provider. This email address should be the same one you used with your old provider. For example, if you used the email address with your old provider, create exactly this same email address with your new provider.

Will my email still work if I transfer my domain? ›

Moving your domain name doesn't mean you have to move your email hosting. Are you using a third party to host your email? If so, it shouldn't be affected by transferring a domain name. does not make changes to the name servers for your domain during the transfer process.

What are the three types of multi-tenancy? ›

There are three multi-tenancy models: Database, Schema, and Table. In Database multi-tenancy, the application connects to a database and gets data while the tenancy logic is delegated to the ops layer.

Is multi-tenant the same as public cloud? ›

Multi-tenancy is synonymous with the term “public cloud”, as the resources used are shared by multiple organizations. This leads to greater efficiency, amazing scalability and lower costs, all of which are huge draws of public cloud computing.

What are the types of multi-tenant architecture? ›

These two types of multi-tenant architectures are the Application layer Multi-tenancy and the Database layer Multi-tenancy.

Can a Microsoft tenant have multiple domains? ›

You can have multiple domains in the same tenant, that's not a problem. And it's the preferred solution when it comes to collaboration, if you use multiple tenants instead there will be certain limitations.

Is SharePoint online multi-tenant? ›

If you have multiple SharePoint Online (Office 365) tenancies that are licensed to use MacroView DMF or Message, you can access all of them in the same DMF session when Modern Authentication has been enabled.

Can you have multiple domains in Office 365? ›

Can I add custom subdomains or multiple domains to Microsoft 365? Yes, typically you can add up to 900 domains to your Microsoft 365 subscription. When you add multiple domains to Microsoft 365, you can host any of the services (like email) on any of the domains you've added.

Can a single tenant have multiple ad directory? ›

You can have only one directory in a tenant at a time.

How many directories can a Azure tenant have? ›

A single user can belong to a maximum of 500 Azure AD tenants as a member or a guest. A single user can create a maximum of 200 directories.

Can a company have multiple Azure tenants? ›

Azure AD B2B collaboration enables users to use one set of credentials to sign in to multiple tenants. For educational institutions, the benefits of B2B collaboration include: Centralized administration team managing multiple tenants.

What is the exchange rule? ›

Exchange Rule means a rule of the National Securities Exchange on which the Common Shares or other securities of the Company are listed for trading.

What is a Microsoft tenant? ›

A Microsoft 365 tenant is a dedicated instance of the services of Microsoft 365 and your organization data stored within a specific default location, such as Europe or North America. This location is specified when you create the tenant for your organization.

What are the 5 requirements for exchange? ›

For an exchange to take place certain conditions must be met:
  • There must be at least two parties.
  • Each must have something that might be of value to the other.
  • Each can communicate and deliver what they are offering.
  • Each is free to accept or reject what is on offer.

What are the three conditions of exchange? ›

Methods of exchange can be grouped into three major types: reciprocity, redistribution, and market. Let's take a brief look at each of these forms of exchange.

What are accepted domains in exchange? ›

Accepted domains are the SMTP name spaces (also known as address spaces) that you configure in an Exchange organization to receive email messages. You use the Exchange admin center (EAC) or the Exchange Management Shell to configure accepted domains in Exchange Server.

How to do tenant to tenant migration in o365? ›

How To Transfer Office 365 Subscription To Another Tenant
  1. The initial step is the purchasing of the individual plan to where one wants to transfer data.
  2. Remove the custom domain from the existing Office 365 subscription.
  3. Set up the custom domain in the new subscription plan.
  4. Cancel the old subscription plan.

How do I set up a Microsoft tenancy? ›

To create a new tenant
  1. Sign in to your organization's Azure portal.
  2. From the Azure portal menu, select Azure Active Directory.
  3. On the overview page, select Manage tenants.
  4. Select Create.
  5. On the Basics tab, select the type of tenant you want to create, either Azure Active Directory or Azure Active Directory (B2C).
Mar 15, 2023

How do you create an organization relationship in Exchange Online? ›

Use the Exchange admin center to create an organization relationship. From the Microsoft 365 admin center dashboard, go to Admin > Exchange. Go to organization > sharing. In new organization relationship, in the Relationship name box, type a friendly name for the organization relationship.

What is my Microsoft tenant domain? ›

Sign in to the Azure portal. Select Azure Active Directory from the menu. The Azure Active Directory Overview page appears. To find the Azure AD tenant ID or primary domain name, look for Tenant ID and Primary domain in the Basic information section.

Does Office 365 automatically save to OneDrive? ›

Available. AutoSave is on by default. All edits automatically sync to your OneDrive for Business cloud. If you turn AutoSave "Off", Save As and Save become available when you select File from the menu.

How do I combine Microsoft 365 tenants? ›

Two steps to merge Office 365 tenants
  1. Plan the merge and check your scope and inventory. If you'd like to move past any migration hiccups, make a detailed plan for the merge. ...
  2. Choose the migration approach and get your new environment ready.
Dec 16, 2022


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