We have a client that has two separate companies, but they want to be able to see each other’s calendar information. Both organizations are on Office 365, but as different tenants. The blog below will walk through the steps on how to set this up. Remember, Free/Busy is a one-way view. If you want both companies to see each others’ calendar, you will need to do this to both.
I will assume that you already know how to open and use Office 365 Powershell. The first step is to allow customizations to occur on our tenant. Enter the following Powershell command:
Second step is to establish a relationship between the two tenants. Modify and enter the following command:
Get-FederationInformation -DomainName <other domain>.com | New-OrganizationRelationship -Name “<company name>” -FreeBusyAccessEnabled $true -FreeBusyAccessLevel AvailabilityOnly
Where <other domain> is the other tenant’s domain (contoso.com) and <company name> is something that you’ve made up to track the relationship (That Microsoft Comapany)
The previous command will only share the basic Free/Busy information. If you want to share other calendar information (location, subject, etc.), then replace AvailabilityOnly with LimitedDetails.
Remember to repeat the above on the other tenant for bi-directional calendar sharing.