If you have two Office 365 tenants that want to share calendars it’s actually quiet easy to setup as the Office 365 tenants are as standard federated with the Microsoft Federation Gateway.

The only thing you need to do is the following. Login in to Office 365 via PowerShell.

Execute the following two lines

Enable-OrganizationCustomization Get-FederationInformation -DomainName <the other cloud-based organization> | New-OrganizationRelationship -Name <the other tenant domain> -FreeBusyAccessEnabled $true -FreeBusyAccessLevel LimitedDetails

The first line enables you to make customization to the Office 365 environment  The second line you have to type in the organisation that you want to share free/busy time with.

Here is an example where mars.com and jupiter.com want to share busy/free time:

– First mars.com runs this command Get-FederationInformation -DomainName jupiter.com  | New-OrganizationRelationship -Name jupiter-federation -FreeBusyAccessEnabled $true -FreeBusyAccessLevel LimitedDetails

– Second jupiter.com runs this command Get-FederationInformation -DomainName mars.com  | New-OrganizationRelationship -Name mars-federation -FreeBusyAccessEnabled $true -FreeBusyAccessLevel LimitedDetails

You’ll also need to adjust the Sharing policy for both domains if you want to share all calendar information. If you don’t you’ll only be able to share free/busy time without any other information. Here is an example:

– First mars.com runs this command Set-SharingPolicy -Identity “Default Sharing Policy” -Domains ‘Anonymous:CalendarSharingFreeBusyReviewer’, ‘jupiter.com:CalendarSharingFreeBusyReviewer’, ‘*:CalendarSharingFreeBusySimple’

– Second jupiter.com runs this command Set-SharingPolicy -Identity “Default Sharing Policy” -Domains ‘Anonymous:CalendarSharingFreeBusyReviewer’, ‘mars.com:CalendarSharingFreeBusyReviewer’, ‘*:CalendarSharingFreeBusySimple’

You’ll now be able to share detailed informatin with another Office 365 tenanat.