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Office 365 Organization Sharing

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Last Modified: 2020-02-26
I've had a request from a client which I thought would be simple however it is turning in to a nightmare.

It is to share calendar free/busy between two Office 365 tenants.

As a proof of concept I've added both domains in each others tenant and the Organization Sharing now shows my two 'federated' Exchange organizations listed.

However calendar information is still not showing between any users cross-tenant.

One of the clients is a hybrid environment with existing on-prem Exchange and one is cloud only.

I've also added each of the Domains in to the Default Sharing Policy in case this was being caused by calendar permissions.

I'm a bit stumped as what is causing this to fail and Microsoft do not seem to have much information on this except how to configure which is already done. I've seen blog posts where people have configured it in the same way as me and it is working.

One thought that I did have was; is any of this affected by conditional access as one of the clients have strict conditional access, but without knowing for sure I do not want to really touch these.

Thanks
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Most Valuable Expert 2015
Distinguished Expert 2019

Commented:
Hybrid requires additional configuration. namely relationships to be created with both the on-premises and the cloud organization. Read here: https://techcommunity.microsoft.com/t5/exchange-team-blog/the-hybrid-mesh/ba-p/605910
And here's also a very detailed series on troubleshooting issues with free/busy: https://techcommunity.microsoft.com/t5/exchange-team-blog/demystifying-hybrid-free-busy-finding-errors-and-troubleshooting/ba-p/607727
Charles HurstContract Senior Consultant

Author

Commented:
Thanks Vasil,

Interesting reads, I did kind of wonder if this was part of the issue, I've found similar articles but they are all the other way around to what I'm trying if that makes sense.

So taking this example in to account:

Company 1 - Cloud only Office 365


Company 2 - Hybrid on-prem 2013 - Office 365 (the free/busy is working between O365 and on-prem)

I'm creating the Organization share between both the companies Office 365 tenants.

So is this issue happening because Company 2's on-prem 2013 Exchange Server is not aware of the relationship with Company 1's Office 365, due to it only being setup in the Office 365 portal?

All users we are testing on are already migrated so are Office 365 mailboxes.

If so, when the migration is finished to Office 365 and the autodiscover record is pointing to Office 365 will that fix this issue, or does the on-prem environment still need to know, it seems strange that an Exchange server purely being used for management would need to be aware just for sharing free/busy between tenants.

Thanks again.
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Most Valuable Expert 2015
Distinguished Expert 2019
Commented:
Yes, switching autodiscover should solve it. Until then, since you are effectively querying both organizations, you need the two relationships.
Charles HurstContract Senior Consultant

Author

Commented:
Excellent, from reading your last comment I suddenly thought to myself rather than actually having to update their DNS autodiscovery could I not just change the endpoint and application URI in the organization relationship to force it to Office 365. Made that change this morning and it's now working!

Thanks for you're help!