Microsoft allows certain permitted senders to automatically add events to your calendar when you receive an email from them. For example, this may be a hotel or flight reservation. Instead of needing to accept a calendar invite, the time in the reservation email is automatically booked out in the Microsoft Outlook calendar.

To see the details of how this concept works and to check if you have it enabled, visit the link below:

https://support.microsoft.com/en-us/office/automatically-add-events-from-your-email-to-your-calendar-32e5cf0c-3e65-4870-9ff9-df3683d3fc97

Certain security checks are performed against these emails to allow the invite to be automatically added. With the implementation of Defend features, the reservation is still received in your inbox and is scanned to ensure the sender has not been compromised.

If you are using Defend features like banners or link rewriting, the invite is not automatically populated into your calendar. However, you can still click on the email to add the reservation. Microsoft is aware of the issue and is working on it.

For now, if you require the functionality, you will need to add an exception to the "Incoming Emails via Defend" Microsoft 365 transport rule:

1. Navigate to the transport rule in Microsoft 365.
2. Select Edit rule conditions > Add a new "Except if".
3. Navigate to Except if > The sender is > This domain.
4. List the domains of the senders you wish to retain the functionality for.

The full list of supported senders can be seen in the link below:

https://support.microsoft.com/en-us/office/supported-senders-for-events-from-email-in-outlook-2c447af8-9e6c-481b-85df-e6d95325d6fd