I get frequent calendar invites that are followed within a few minutes by a cancellation for the meeting.This happens about once per day. I suspect this is a technique to confirm valid email addresses. Norton's Outlook plug-in won't handle these.
I delete the appointment(s) and all future appointments in Outllook and do not send feedback. I then send the email (unopened) to spam folder, but appointments continue to appear on my calendar ad infinitum.