2 Tenants with 1 Active directory forest

[jennylee]

From what I read, you can't have 2 tenants with 1 active directory forest or is there a way to set that up?  They need to send email back and forth between the tenants, share calendars, same address list etc. Basically act as 1 tenant.

[#2]

Hi Jennifer,

That's not possible, you cannot have the same public domain registered in two tenants.

But is possible to have a split sync between 2 tenants with 1 active directory forest.

Here you have an article that shows the scenarios https://docs.microsoft.com/en-us/azure/active-directory/connect/active-directory-aadconnect-topologi...

[#3]

So you have to purchase Azure AD connect instead of doing the DirSync in the tenant..correct? Does this also replace the single sign on AD FS?

[#4]

Hi Jennifer,

Azure AD Connect is the current version, DirSync is discontinued.

You can chose the method of authentication based on your requirements you can have ADFS or just AD Connect. 

[#5]

---

@jennylee wrote:

From what I read, you can't have 2 tenants with 1 active directory forest or is there a way to set that up?  They need to send email back and forth between the tenants, share calendars, same address list etc. Basically act as 1 tenant.

---

Why are you trying to split an organization into two tenants? Perhaps if you explain your requirements in more detail we can provide a better response.

[#6]

Apparently it costs a lot more for licensing to have all of our users in 1 tenant ( 600 users). If you keep it to 300 its cheaper. We are non profit but do not qualify for non profit licensing so my Boss wants to split them. I believe she said you have to pay for an E3 license for all in 1 tenant and you can do a Business premium for a lot cheaper but you can only have 300 in a tenant. I would love to only do one tenant.

[#7 · Accepted solution]

Yeah that's not a very good reason. It costs what it costs, basically. If you're larger than the small business tenants allow, then you need to pick from the enterprise plans. That's assuming you want all the features of those plans.

Enterprise E1 is fine for some customers who don't want the Office desktop suite. Some customers also do just fine buying Exchange Online licenses + Office 365 ProPlus licenses, which comes out to less overall than a full E3 license. You might even have a combination of different users, e.g. some that need E3, some that only need Exchange Online, maybe even some that qualify as "Firstline workers".

Splitting into two tenants, aside from the technical impossibility of having the same email domain in two tenants, only adds to the complexity of the overall solution and makes it difficult to properly collaborate across tenants. You'll lose more in time wasted than you'll save on licenses.

Hopefully your boss comes around and accepts the best solution of a single tenant.

[#8]

Thank you. After a discussion and a call with a vendor, she agreed to go with office online and various versions of office licensing. The main goal was to get away from exchange on premise.

I'm quite relieved I don't have to try to figure out some impossible configuration.  Thanks for the ammunition!

[#9]

That's good news :)

[#10]

Great news !

[#11]

I'm sorry I'm having problems finding documentation to do a hybrid migration from 2010 on premise to exchange online as all the documentation keeps referring to migration to Office 365. We are not buying office 365 now. Not sure where to ask this question or if the migration to O365 is the same thing. Thanks

[#12]

It's the same thing. Office 365 is the entire suite of apps and services (Exchange Online, SharePoint Online, Skype for Business, Teams, etc). If you're just buying Exchange Online licenses you still have an Office 365 tenant, just without most of those other services.