(I'm using Outlook 2013 and Exchange 2013.)
Based on very poor support I got from Microsoft a long time ago, I was advised to export my Exchange mailbox and then create a new one and re-import. This caused nothing but problems the biggest of which is that I am now stuck with incessant reminders on calendar events (meetings.)
When I "Dismiss" an event that has passed the dismissal seems to generate another reminder (not another event on my calendar, just the reminder.) Also, I think it's only the original reminder which, when dismissed, generates another reminder and that one itself, along with all the duplicates, continue to popup.
Over time I end up with more and more reminders for a single event and it's driving me crazy. I've now got 40 and 50 reminders (per calendar event) that I have to dismiss over the course of every day.
I've tried starting Outlook with
/cleansniff on multiple occasions. They do nothing.