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Victor Rosas
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Office 365 Cross-tenant trust relationship, what works and what doesn't?

I'm trying to get an understanding of the impact of having an Office 365 Cross-tenant trust relationship, the pro's and con's, what's going to work and what's totally going to fail. Do you have examples of real-world setups on this? 

Microsoft 365Active Directory* Azure AD* b2b

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Victor Rosas

8/22/2022 - Mon
Vasil Michev (MVP)

You have to be a bit more specific here, which functionality are you referring to exactly? Federation, org relationships, plain old B2B policies? Microsoft is now previewing the so-called cross-tenant access policy, which will likely be the way going forward, but afaik that's not even public yet, so not something we should be discussing here.
Victor Rosas

First off, thank you for your time and feedback. Let me try to give a little context. Our company is in the process of absorbing another smaller company that it has recently acquired, so we have been tasked to merge them over from their Google environment over to our On-premise Full Hybrid Microsoft Exchange, Microsoft 365 tenant, Azure AD environment. However, as they are somewhat of a smaller company, 80 users, and to minimize the migration complexity, we thought to migrate them over to their own on-premise AD and Microsoft 365 tenant, then setup a trust relationship between their Microsoft 365 tenant and ours.

However, in trying to do some research, on how user collaboration may be impacted in a Microsoft 365 multi-tenant setup, I came across comments like this: "One of the most important things to consider before deciding between a single or multiple tenants is the end user experience. The user experience with multiple tenants will always be limited in comparison with the end user experience with a single tenant. ." (https://blogit.create.pt/miguelisidoro/2019/01/07/pros-and-cons-of-single-tenant-vs-multiple-tenants-in-office-365/) . This blog post is really good at making a case for trying to setup both organizations under a single tenant, but it's from 2019.

So, I've come across some recent Microsoft articles covering Azure Active Directory (Azure AD) B2B that seem to provide some information on how users can collaborate in a Microsoft 365 multi-tenant setup (https://docs.microsoft.com/en-us/microsoft-365/enterprise/microsoft-365-inter-tenant-collaboration?view=o365-worldwide) .

That's really where my original question lies, initially it appeared that cross tenant collaboration was difficult, but recently it has vastly improved with tools like Azure Active Directory B2B and even more recently Cross-tenant mailbox migration (preview) (https://docs.microsoft.com/en-us/microsoft-365/enterprise/cross-tenant-mailbox-migration?view=o365-worldwide ), is that assumption correct? Organizations can now safely setup multiple business entities under their own tenants without compromising on cross-tenant collaboration, or are there certain workload like Exchange Online, Sharepoint, or Teams that may still be impacted by having a mutl-tenant setup?

Vasil Michev (MVP)

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Victor Rosas

Thanks for the feedback was looking for some validation on this topic from an industry leader. It does appear that multi-tenant setups are more complex and the tools to aid in collaboration are fairly new. 
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