During the recent Microsoft Ignite conference I heard questions related to hybrid and partner free/busy relationships quite often, so I wanted to write about it. This scenario applies to companies with one or more external free busy relationships configured. For instance, you could have two or more companies on-premises sharing free/busy between each other. Then one fine day, one of the companies deploys a hybrid configuration and moves mailboxes to Office 365; in our example, it is Tailspin. Suddenly, Contoso and Fabrikam users find availability information is not showing for the Tailspin mailboxes moved to Exchange Online. This blog post discusses why free/busy is broken and what you can do about it.
Note: OAUTH is not a supported way to see free/busy between two on-premises organizations.
Note: In most environments, the shared namespace “TailspinToys.com” can be used as the Target address for on-premises users and you would not need the additional namespace of onprem.TailspinToys.com. However, to account for all complex partnerships that could be in place, a unique namespace used as the target address will ensure free busy works properly.2. Create an Organization Relationship between Contoso on-premises and Tailspin in Exchange Online. For this Organization Relationship the domain name should be TailspinToys.Mail.onmicrosoft.com. 3. Make sure that you have a solution in place to sync mailbox enabled objects between Tailspin and Contoso. As a mailbox is moved from Tailspin on-premises to Tailspin online, Contoso needs to be made aware and the related objects’ Target Address needs to be updated in Contoso. This is needed to ensure we direct the free/busy requests to the correct premises the first time. This step can be achieved via Forefront Identity Manager (FIM) or with a script.
Note: The domain name “TailspinToys.com” is not present in any of the Organization Relationships in the Contoso environment. Keeping this name out of the Organization Relationship will ensure that you can continue to use the shared namespace and see free/busy information.
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