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What will happen if I move an existing domain from another Microsoft 365 tenant to another existing Microsoft 365 tenant?

Roose Chua 0 Reputation points
2026-01-05T08:07:06.7133333+00:00

Hi There,

Currently, our small organization is subscribed to 2 Microsoft 365 tenants (mostly Microsoft 365 Business Standard users), with each using its own domain name. These 2 tenants and their domain names has been existing for more than a year already. For example:

Tenant A | abc.com

Tenant B | def.com

Now, they want to combine these 2 domains only under Tenant A. I am aware that we can add multiple domains under 1 tenant and use one of the domains for their email alias, but I am unsure of the following:

  1. How can we migrate the user emails from Tenant B once we add the def.com domain to Tenant A/abc.com?
  2. When our original Tenant B users, which will now have the abc.com email address, and the def.com as their alias, invite guests into Teams meetings, which email address will be shown in Teams to the meeting attendees? It is important that the guest attendees still sees them with the def.com email address for our use case.

Can anyone provide me their similar experience with this and how they did it? Appreciate the help and support in advance! Thanks!

Moved from Microsoft 365 and Office | Other

Microsoft 365 and Office | Install, redeem, activate | For business | Other
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  1. Doris V 1,695 Reputation points Microsoft External Staff Moderator
    2026-01-07T04:27:24.7666667+00:00

    Hello @Roose Chua, 

    Thank you for posting your question in the Microsoft Q&A forum. 

    Based on your description, you're working with two existing Microsoft 365 tenants and planning to consolidate the domains under Tenant A. This is a common scenario in tenant‑to‑tenant consolidation, and I will address your questions step by step. 

    For your scenario, Microsoft provides two official articles that outline the recommended process for moving data, users, and domains between tenants. These resources explain the end‑to‑end steps, supported migration paths, and best practices: 

    1. Cross‑Tenant Migration (Microsoft FastTrack) 

    This article provides Microsoft’s official framework for moving users, mailboxes, and identities between Microsoft 365 tenants, including prerequisites, planning, coexistence, and supported workloads.  Reference: Cross-Tenant Migration 

    1. Data Migration Guidance 

    This guide covers additional workload migrations such as SharePoint Online, OneDrive, Teams, and other service data that may need to be moved when consolidating tenants.  Reference: Data Migration 

    Before starting any tenant‑to‑tenant consolidation, it’s essential to follow a well‑structured and methodical approach. This overview pipeline reflects the most effective way to plan and execute the process: 

    1. Pre‑migration planning 
    • Inventory users, mailboxes, OneDrive and SharePoint content. 
    • Determine whether domain migration is required and in what sequence. 
    • Confirm licensing availability in the target tenant. 
    1. Prepare both tenants 
    • Verify domain ownership. 
    • Configure identity synchronization / Entra ID settings if required. 
    • Establish coexistence rules for email, Teams, and OneDrive. 
    1. Migrate workloads based on your needs 
    • The process depends on what you need to move: 
    • Exchange Online mailboxes (CTUDM recommended) 
    • OneDrive (cross‑tenant capabilities or migration tools) 
    • SharePoint Online (site‑level and library‑level migrations) 
    • Teams (channels, chats, memberships) 
    1. Move the domain 
    • If you want to move def.com from Tenant B to Tenant A: 
      • Remove the domain completely from Tenant B first (users, aliases, DNS). Then add it to Tenant A. 
    1. Post‑migration validation 
    • Test mail flow, login, Teams meeting identity display, and file access. 
    • Confirm that all users show the correct primary SMTP domain. 

    Important: Manual migration between Microsoft 365 tenants can be technically challenging and may require significant coordination. The complexity depends entirely on which workloads you plan to migrate. Manual processes become difficult when handling: Domain moves, SharePoint/OneDrive, Microsoft Teams data and Large Exchange Online mailboxes 

    If you find the cross‑tenant migration process challenging at any stage, you can open a support ticket directly through the Microsoft 365 Admin Center for further assistance: 

    1. Navigate to https://admin.microsoft.com 
    2. Sign in using your Global Admin or Admin account. 
    3. Select Support 
    4. Click “New service request” or “Create a ticket” 
    5. Provide a clear title and describe the issue including both tenant name/domains, what you are trying to migrate, steps or any errors encountered (if any). 

    Reference: Get support - Microsoft 365 admin 

    The support team can help guide you through the required steps or connect you with the appropriate resources to ensure a smooth and successful migration. 

    Note: Please understand that as a forum moderator, my primary goal is to provide helpful guidance and support through general troubleshooting steps. While I don’t have access to internal systems or test devices required to resolve backend/account issues, I truly appreciate your understanding of these limitations. I genuinely hope the information helps you in the right direction, and we are always here to assist as much as I can within our scope.   

    I hope this information is helpful. Please follow these steps and let me know if it works for you. If anything is unclear, please don’t hesitate to reach out to me. 

    Thank you for choosing Microsoft, and I am looking forward to your response. 

     If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have any extra questions about this answer, please click "Comment."    

    Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread. 

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  2. ppavle 5,200 Reputation points Volunteer Moderator
    2026-01-05T10:18:31.9133333+00:00

    You can have some users using @def.com as primary email address and some @abc.com on the same tenant. In Teams, primary email will be displayed.

    Regarding Migration, i would hire someone to do it, or use 3rd party tools. Not to promote any of them, you can easily find them.

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