We have made major updates to improve the way Outlook for Windows connects to and updates shared calendars. These improvements are available for Outlook 365 customers with the latest Monthly Enterprise Channel, Current Channel, or Semi-Annual Enterprise Channel update.

Note: While the shared calendar improvements are available in the Semi-Annual Enterprise Channel, we strongly recommend placing your users on the Monthly Enterprise channel or Current Channel.

This article provides details about how to turn on and turn off these shared calendar improvements in Outlook for Windows. 

For technical details about what is changing with calendar sharing in Exchange Online or other Outlook applications, see Calendar Sharing in Microsoft 365.

Turn on shared calendar updates

You can enable the improvements for a single user in Outlook for Windows, or you can use a Group Policy to enable them for all or some users in your organization.

Enabling the shared calendar improvements does not impact your experience with your own calendars.

Enable for a single user

We have introduced a new option in the Exchange Account Settings dialog: Turn on shared calendar improvements.

Note: This option will only be available to people using Exchange Online. There are no changes to shared calendars when one person's calendar is hosted in Exchange on-premises..

  1. In Outlook, select File >Account Settings >Account Settings.  You will see a list of your email accounts.

  2. Select the Microsoft Exchange account that you use to manage someone else's calendar and choose Change...

  3. Choose More Settings, followed by the Advanced tab.

  4. Select the checkbox next to: Turn on shared calendar improvements.
    You can turn on the shared calendar improvements with a checkbox.

  5. Close and restart Outlook.

Opting into these improvements do not impact your experience with your own calendars and you can go back at any time.

Enable using Group Policy

In addition to the new option, IT admins can use Group Policy to configure how Outlook connects to shared calendars.

We have introduced a new Group Policy setting: REST updates for calendars. This setting is available in the Group Policy Administrative Template files (ADMX/ADML).

  • [HKCU\Software\Policies\Microsoft\Office\16.0\Outlook\Options\Calendar]

  • Policy enabled: “SharedCalendarImprovements”=dword:00000001

  • Policy disabled: “SharedCalendarImprovements”=dword:00000000

When this new policy is enabled:

The Turn on shared calendar improvements checkbox is enabled for all users. The UI checkbox is checked and disabled, so end users cannot turn off the improvements.

When this new policy is disabled:

The Turn on shared calendar improvements checkbox is disabled for all users. The UI checkbox is unchecked and disabled, so end users cannot turn on the improvements.

Confirm that your shared calendar is using the new improvements

In order to benefit from the improvements, the setting must be enabled in Outlook for Windows and your shared calendar must be upgraded to the new sharing platform in Microsoft 365.

You can check whether your shared calendar is upgraded using Outlook for Windows or using PowerShell.

Using Outlook for Windows

For any calendar on which you have Editor or Delegate permissions, Outlook for Windows will tell you if the calendar has been upgraded to the new sharing platform.

After the setting has been enabled and you have restarted Outlook, you can view the Calendar Properties dialog to check whether you are using the new improvements. If you have been upgraded, you will see “Type: Folder containing Calendar items (REST)”.

Upgraded to new sharing platform

Not yet upgraded

You can use the Calendar properties to confirm if you're using the REST or MAPI interfaces.

You can verify if your calendar is using the new REST interface or MAPI interface.

Remember that you will only see the REST or MAPI annotation if you have Editor or Delegate permissions to the calendar.

Some versions of Outlook will also show “(preview)” next to shared calendars that have been upgraded. We are phasing out this label, in favor of the Properties dialog.

Using PowerShell

To confirm whether the calendar is on the new sharing platform, you can check the ExtendedFolderFlags in the output of Get-MailboxCalendarFolder.

If the ExtendedFolderFlags includes "SharedIn", the calendar is on the new sharing platform.

Is your shared calendar not yet upgraded?

If your shared calendar is not yet on the new sharing platform in Microsoft 365, you can upgrade the shared calendar manually. This requires that the shared calendar owner is hosted in Exchange Online, and they have specifically granted you permissions to their calendar. If these conditions are met, follow the instructions below to remove and re-add the shared calendar.

Remember that the shared calendar improvements are only available for calendars shared between people using Exchange Online.

  1. Navigate to the Calendar module and find the shared calendar you want to upgrade.

  2. Right-click on the shared calendar and select Delete Calendar.

  3. Close and restart Outlook.

  4. From the Home ribbon in the Calendar module: Choose Open Calendar > Open Shared Calendar

  5. Enter the name of the person who has shared their calendar with you

  6. Click OK to close the dialog.

  7. The shared calendar will reappear in your Calendar list and should now be upgraded.

IMPORTANT: Immediately after adding the calendar, the calendar might appear empty. It takes a few minutes to setup the new shared calendar and sync over all the calendar events. This delay occurs only on the initial setup of the new shared calendar, and you will not see any more delays once the initial sync completes. In the case of very large calendars, it can take a few hours to sync over all the calendar events.

Turn off shared calendar updates

If you tried the shared calendar improvements, but they didn't work for you, please let us know through Outlook in-app support.

To turn off the shared calendar improvements, follow the same instructions as above, and unselect the checkbox next to: Turn on shared calendar improvements.

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