Single Sign On to different O365 tenants

Christoph Nellis 0 Reputation points

Hi everybody,

I have the following situation:

  • Single Active Directory domain (domain.local)
  • 2 Office 365 tenants (,
  • 2 ADFS Servers
    • one of them syncing users from one OU1 to and handling SSO. Users have UPN Suffix in active directory
    • the other one syncing users from OU2 to and handling SSO. Users have UPN Suffix in active directory

Now the problem is that we have users in each domain which are having mailboxes on both tenants. Currently these users have 2 active directory users. I would like to change this, so the people just need 1 active directory user. Is there any way to accomplish this? I appreciate any input, have been fiddling around with this but can not find a solution on this problem.

Thanks everybody in advance for your time!



Microsoft 365
Microsoft 365
Formerly Office 365, is a line of subscription services offered by Microsoft which adds to and includes the Microsoft Office product line.
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Active Directory Federation Services
Active Directory Federation Services
An Active Directory technology that provides single-sign-on functionality by securely sharing digital identity and entitlement rights across security and enterprise boundaries.
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Microsoft Entra ID
Microsoft Entra ID
A Microsoft Entra identity service that provides identity management and access control capabilities. Replaces Azure Active Directory.
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  1. Akhilesh 6,115 Reputation points Microsoft Vendor

    Hi @Christoph Nellis

    Thank you for your post!

    I understand that you are looking for a way to have a single Active Directory user for users who have mailboxes on both of their Office 365 tenants.

    You can migrate mailboxes from one Microsoft 365 or Office 365 organization to another

    If you want collaboration and access to applications across different tenants, while maintaining the organization’s ability to evolve and manage user lifecycles efficiently you can use Cross-tenant synchronization This feature is particularly useful for organizations that own multiple Microsoft Entra tenants and wish to streamline intra-organization cross-tenant application access.

    Also, you can use Microsoft Entra B2B collaboration which allow organizations to securely share their applications and services with external partners and guests.


    Hope this helps. Do let us know if you any further queries.


    If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.