Preparing Microsoft and Google Tenants for Admin-Managed Syncs

CalendarBridge does not store any calendar data; it only syncs availability into an existing calendar on the destination tenant. Therefore, each person/resource whose availability should be visible on a tenant must have a calendar object on that tenant. This article walks you through setting up calendars and accounts so you can sync availability between tenants.

C Chad Updated October 17, 2025 4 min read

Example scenario

Company X operates in a split environment:

Current problem: Users in one tenant cannot see the free/busy (availability) of users in the other tenant. Goal: Allow cross-tenant availability visibility. For example, john.doe@contoso.com (M365) should be able to see the availability of sarah@example.com (Google), and vice versa if desired.

Concrete example: John (M365) needs to see Sarah (Google)

  1. Source (Google): Sarah’s primary calendar at sarah@example.com.
  2. Destination (M365): The contoso.com tenant must have a calendar representing Sarah — either a full user mailbox sarah@contoso.com (requires an M365 license) or, recommended, a resource mailbox named “Sarah” to avoid licensing a new user.
  3. CalendarBridge then syncs Sarah’s availability from Google → into the “Sarah” calendar on M365, so John (and other M365 users) can view it.
  4. If users on contoso.com will invite Sarah’s calendar to meetings, Sarah also needs a reverse sync connection (M365 → Google) so accepted meetings on the “Sarah” resource calendar are written back to her actual sarah@example.com calendar.

Reverse direction: Sarah (Google) needs to see John (M365)

  1. Source (M365): John’s primary calendar at john.doe@contoso.com.
  2. Destination (Google): The example.com tenant must have a calendar representing John — either a full user mailbox john.doe@example.com (requires a Workspace license) or, recommended, a resource calendar named “John Doe” (no user license needed). Google assigns a resource address like c_188bp5b5u2np4ghmh4psh6ra7lfl6@resource.calendar.google.com.
  3. CalendarBridge then syncs John’s availability from M365 → into the “John Doe” resource calendar on Google.
  4. If users on example.com will invite John’s calendar to meetings, John also needs a reverse sync connection (Google → M365).
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Summary. For each direction you want visibility or invitations to flow, create (or reuse) a corresponding calendar on the destination tenant and configure a CalendarBridge sync for each direction. Visibility only → one-directional sync. Visibility + event invites → two-directional sync (one in each direction).
DirectionSourceDestinationDestination calendar neededNotes
Google → M365sarah@example.comcontoso.comUser mailbox or resource mailbox “Sarah”If M365 users will invite “Sarah,” also add reverse sync (M365 → Google)
M365 → Googlejohn.doe@contoso.comexample.comUser mailbox or resource calendar “John Doe”If Google users will invite “John Doe,” also add reverse sync (Google → M365)

Creating the necessary calendars on the destination tenant

On the destination tenant (where people need to view or invite the user), create a calendar that represents that person or resource.

  1. Microsoft 365 destination: create a user mailbox (requires an M365 license) or a resource mailbox (no license needed) for the person/resource. Resource mailboxes automatically receive a standard email address that CalendarBridge can use (e.g., confroom1@contoso.com), so no additional service account or sharing configuration is required.
  2. Google Workspace destination: each calendar can be a user mailbox (e.g., john.doe@example.com) or a resource calendar. Resource calendars in Google do not have a usable email address (they look like c_…@resource.calendar.google.com), so a service account must be created:
    1. Create a service account in the Google Workspace tenant (e.g., cb_svc@example.com).
    2. In Google Calendar, logged in as a super admin, open the resource calendar’s Settings and sharing.
    3. Share the calendar with the service account and grant Make changes and manage sharing permissions.
    CalendarBridge can then connect using the service account email address to sync to and from that resource calendar.
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Summary. Microsoft 365 resource calendars have normal @contoso.com addresses — no service account needed. Google Workspace resource calendars have @resource.calendar.google.com addresses — create and share with a service account (e.g., cb_svc@example.com).