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Blue Tongue
Asked: 2020-03-05 03:47:36 +0800 CST

UPN Confusion in a 1x AAD 2x Forest 1x O365 tenant scenario

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We have the following scenario:

Company A

Forest = CompanyA.com

Domain = CompanyA

Email Domain CompanyAX.com

Users' UPN = CompanyAx.com

Company B

Forest = CompanyB.com

Domain = Corporate

Email Domain = CompanyB.com

Users' UPN = CompanyB.com

There is a inter-forest trust between the 2x forest already.

We plan to install 1x AAD Connect to link up the 2x Forest.

The 1x AAD Connect will link up to 1x O365 tenant.

Email domain of the O365 tenant will be CompanyC.com

I think the above is doable.

However, I couldn't understand once the 2x forest sync up to Azure AD, what will the users use to log on to O365?

Can they still use their original UPN like [email protected] and [email protected]?

Or all of them need to use [email protected]?

Hope someone can enlighten me. Thanks heap!

microsoft-office-365

1 Answers

    1. A Forest Trust isn't required for this scenario. You may have the trust for other reasons but it isn't required for syncing the users to the same Office 365 tenant.

    2. If both domains are verified in your Office 365 tenant then the users current UPN will become their UPN in Office 365. So the answer is they will use their original UPN as their Office 365 login.

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