Resolve Full Access and delegate conflicts on legacy calendars

Summary

Resolves Outlook calendar errors when a user has both Full Access and delegate permissions on a calendar that uses the legacy MAPI sharing model. Remove and re-add the shared calendar to move it to the modern sharing model and verify that the folder type includes (REST).

Symptoms

• A user has both Full Access to a mailbox and delegate access to its calendar.
• Outlook shows inconsistent calendar permissions, synchronization failures, or access errors.
• In classic Outlook, the shared calendar folder properties don't show (REST).

Cause

Full Access and Outlook delegate permissions can coexist when the calendar uses the modern shared-calendar model. The combination isn't supported on the legacy MAPI sharing model.

Resolution

1. Confirm that both mailboxes are hosted in Exchange Online.
2. In classic Outlook, open the shared calendar folder properties and confirm whether the folder type includes (REST).
3. If the calendar uses the legacy model, remove the old shared-calendar entry from Outlook.
4. Add the calendar again by using Add Calendar > Open Shared Calendar, or have the mailbox owner send a new calendar-sharing invitation.
5. Open the folder properties again and confirm that the folder type includes (REST).

For information about the legacy conflict, see Conflicting permission sets when working with shared or delegated folders in Outlook. For information about the modern model and upgrade behavior, see Calendar sharing in Microsoft 365.

Verify the resolution

Confirm that the user can open the mailbox through Full Access and manage the calendar as a delegate without synchronization or permission errors.

More information

• Restore private calendar access
• Resolve hybrid delegate failures