Hello Niclas Nibbe,
Thanks for your post in Microsoft community. Some versions of Microsoft Outlook may not import the list of optional and required attendees for each meeting. Outlook 2007 and Outlook 2010 successfully import both required and optional
attendees when using iCalendar format (*.ics). From our end we have tried to search but we didn’t found any way to achieve your requirement. We are not able to import " required attendees" in appointments from Excel to Outlook Calendar.
However, regarding this feature, as we have found that currently very few users have voted for this feature via our UserVoice service:
https://outlook.uservoice.com/forums/322590-outlook-2016-for-windows/suggestions/39413818-exporting-appointments-from-excel-to-outlook-calen . Therefore, we'd like to recommend you that kindly give your vote and also post your comment on this feature as
per your requirement via above mentioned UserVoice link. Because many features and services are built on the basis of customers' feedback, vote or comment via UserVoice service and Microsoft is always focus on customers' feedback, vote and comment. Also, on
the basis of customers' good idea and experience some new features and services would be added in future and for that your good and valuable ideas will be very helpful for them to improve the service and product.
Thanks and regards,
Ankita Vaidya