Office 365 (Known Issues) - PantherLISTs Not Recognized for Meeting Invitations
Outlook does not recognize PantherLISTs as containing members that can be invited to meetings, and therefore PantherLISTs cannot be used.
Resolution Status: Unresolved
can enter each attendee in the meeting invite or create a contact group
containing all attendees and invite the entire group. Instructions for
creating contact groups are available on Microsoft's People overview page under the "Create a Group" heading.