Apple Calendar no longer discovers newly shared Microsoft 365 Exchange Online calendars
We are experiencing an issue with Apple Calendar when accessing shared calendars hosted in Exchange Online.
Until recently, users were able to add newly shared calendars without any issues. Without any known changes to our Exchange Online configuration, newly shared calendars are no longer discovered or displayed in Apple Calendar.
The issue occurs consistently for all tested users.
Steps to Reproduce
Grant calendar permissions to a user for a shared mailbox.
Add the Calender to "My Calenders" in OWS
Sign in to Apple Calendar using the user's Microsoft Exchange account.
Attempt to access or add the shared calendar.
Expected Result
The shared calendar should appear in Apple Calendar and be accessible, as it did previously.
Actual Result
The shared calendar can be added successfully in Outlook (Desktop).
The shared calendar can be added successfully in Outlook on the Web (OWA).
The shared calendar is not displayed or discoverable in Apple Calendar.
An additional observation is that calendars which had previously been added to Apple Calendar continued to work correctly. However, once such a calendar is removed from Apple Calendar, it can no longer be added again.
Troubleshooting Performed
The following has already been verified:
The issue is reproducible on multiple iPads.
The issue is reproducible with multiple user accounts.
The issue is reproducible with multiple shared mailboxes.
Calendar permissions have been verified.
Exchange Web Services (EWS) is enabled.
Both mailboxes are configured as Shared Mailboxes.
The calendar folders exist and are functioning correctly.
Access through Outlook and Outlook on the Web works without any issues.
Additional Information
Both mailboxes are Exchange Online Shared Mailboxes.
The calendars can always be opened successfully in Outlook and Outlook on the Web.
The issue only affects Apple Calendar.
No intentional changes were made to the Exchange Online configuration before the issue started.
The behavior is consistent across multiple Apple devices and multiple user accounts.
We would appreciate your assistance in determining whether this is a known interoperability issue between Exchange Online and Apple Calendar.
Thanks.
iPad, iPadOS 26