Sync Outlook with Google Calendar and other Microsoft 365 tenants
Outlook and Google Calendar have no built-in two-way sync. Caltsu adds one: each calendar gets a Busy block for every event in the other. Consultants often hold an account in each client's Microsoft 365 tenant. Caltsu connects them all, so every client sees when you are booked elsewhere. The block names the source calendar, so rename calendars you do not want a client to see.
Accounts you can connect
| Account type | What Caltsu syncs |
|---|---|
| Microsoft 365 | Work or school accounts in any tenant, including accounts a client issued to you. Caltsu syncs the account's default calendar. |
| Outlook.com | Personal Microsoft accounts, including Hotmail and Live addresses. |
Permissions Caltsu requests
| Scope | Why Caltsu needs it |
|---|---|
| openid, email, profile | Identifies which Microsoft account you connected. |
| Calendars.ReadWrite | Reads events from the default calendar and creates, moves and deletes Busy blocks. Caltsu uses the start, end and status, keeps the subject in a change fingerprint, and checks the body preview to recognise its own blocks. Delegated, so it covers only the signed-in user's calendars. |
| offline_access | Keeps sync running when you are not signed in to Caltsu. |
Admin consent in Microsoft Entra
Each Microsoft 365 tenant decides whether users may consent to apps themselves. If yours does not, the Microsoft sign-in asks for administrator approval, or sends a request to your admins if the tenant uses the admin consent workflow.
An administrator can grant consent once for the whole tenant. Caltsu asks for delegated calendar access only. It does not request mail, files, Teams or directory access, and it acts only on the calendars of the user who signed in.
- 1Entra ID > Enterprise apps, or Identity > Applications > Enterprise applications in older layouts
- 2Open Caltsu. It appears after the first sign-in attempt from your tenant
- 3Security, then Permissions
- 4Grant admin consent for your organization
Setting it up
- 1
Start a trial and open the dashboard.
- 2
Choose Connect account, pick Microsoft and sign in on Microsoft's own page. Repeat for each tenant and each Google account.
- 3
Add the calendars to your sync group. Blocks for existing events appear, and later changes arrive through Microsoft Graph change notifications.