Retain Meeting Invitation emails
If you would like to retain meeting invitation emails after they have been accepted or declined, you merely need to change an Outlook Options setting.
Step One
Open Outlook and click the File tab and select Options on the left side of the Backstage View.
Step Two
In the Outlook Options dialog box, select Mail from the categories list on the left.
Step Three
Scroll down to the “Send messages” category and uncheck the option labeled “Delete meeting requests and notifications from Inbox after responding”.
From this point forward, when you accept or decline a meeting request, the original invitation will remain in your Outlook Inbox so you can refer to it when you need to refresh your memory as to its details.