Two Ways to Let Office 365 Tenants Share Calendars: Sharing Policies vs. Org Relationships

When a client needs to collaborate with an outside organization, or when you as the MSP need shared visibility into a client's calendars, Exchange Online gives you two separate controls to do it. They are easy to confuse, and the defaults are more permissive than most owners realize. This is the overview of how inter-tenant collaboration works in Exchange Online: what the two mechanisms are, what is already turned on, and where to configure each one. It is the first in a series covering the different ways Office 365 supports cross-tenant collaboration.

What are we actually trying to enable?#

The goals of inter-tenant collaboration usually come down to:

• A central location for files and conversations
• Sharing of calendars
• Using instant messaging
• Audio and video calls for communication
• Securing access to resources and applications

This article focuses on the Exchange Online piece: calendar and free/busy sharing.

The two collaboration mechanisms in Exchange Online#

Exchange Online defines collaboration through two different policy types, and choosing the right one is the whole game.

Business-to-business: organization relationships#

Business-to-business sharing is set up by creating organization relationships. This is the right mechanism when two organizations want a defined, scoped relationship between their tenants.

User-to-user: sharing policies#

User-to-user sharing is set up by creating sharing policies. This governs what individual users are allowed to share externally.

What is already turned on by default#

Before you change anything, know the starting state. By default:

• There is no organization relationship set up.
• Users can share free/busy info with external users.
• Users are allowed to send access to their calendars to anonymous users with an email invitation.

Adjusting the basic calendar defaults#

In the admin portal#

The first option is to open the admin portal and go to Settings > Services & Add-Ins.

Open Calendar settings#

Select "Calendar" to view the default settings.

Creating a granular sharing policy#

Go to the Exchange Admin Center#

For more granular policies, go to Admin Centers > Exchange Admin Center.

Open the Organization tab#

Click Organization on the left-hand side to view or add new sharing policies.

Define how much detail leaves the tenant#

You can choose to:

• Share free/busy with time only
• Share free/busy with time, subject, and location
• Share all info including time, subject, location, and title

Creating an organization relationship#

In the Exchange Admin Center#

Creating an organization relationship happens in the same place as creating an individual sharing policy.

Define the policy#

Choose your settings and the external domains you want to create a relationship with.

Scope it to specific users#

Choose the groups of users that are allowed to share with this organization.

Between sharing policies for user-level detail and organization relationships for scoped business-to-business sharing, you have the granularity to enable exactly the collaboration a client needs and nothing more. The catch worth remembering is that the permissive defaults are on from day one, so external calendar exposure is something you opt out of, not into.