Old SharePoint calendars should be removed from your Outlook. This is especially important as we move away from AG SharePoint sites to Office366 SharePoint sites. This How To explains how to delete/remove connection to a SharePoint calendar in your Microsoft Outlook application.

To delete a connection to a SharePoint calendar:

  1. Open your Outlook application.
  2. Click the Calendar icon at the bottom left of the screen to open your calendars.
  3. In the left navigation pane, locate the SharePoint calendar you wish to delete.
  4. Right-click and choose Delete Calendar.
  5. If prompted “Do you want to delete the [calendar name] folder and its contents? Deleting this folder…", click Yes.

NOTE: This does not delete the calendar from SharePoint.