On Windows
If you are using the Outlook application on Windows, you can turn off automatic deletion of meeting invites, so the invite will continue to show in your inbox even after you've responded.
- Go to File tab.
- Click Options then Mail.
- Under Send messages section, uncheck Delete meeting requests and notifications from Inbox after responding.
On Mac
There is currently no settings to stop auto-deleting the accepted meeting invite in Outlook for Mac. Once you have accepted a meeting invite, you can find it in the Outlook Calendar.