This is an option from Microsoft Outlook that synchronizes all your subscribed RSS feeds. You can turn this off by right click on the Inbox folder which is the root of all you e-mail folders > IMAP Folders option > click on query button. Go to the Subscribed tab, select and click the Unsubscribe button on all your undesired folders. Make sure you are subscribed to Inbox, Inbox.Send and Inbox.Trash.