Hi @RobinC ,
Based on my research, the correct is AutoDismissPastEvents.
Create this key value in the registry and restart Outlook, click Send/Receive > Update Folder.
Reminders of past events pop up.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.