To enable/disable the Recent Campaigns RSS Feed click on your User Settings in the upper right-hand corner or the RSS Feed button above Recent Campaigns.
This will bring you to your User Settings page. Scroll down to Account Features and find the Recent Campaigns RSS Feed. Click on the button to enable/disable an RSS Feed of recently sent campaigns. This feature is only available to paid accounts and can only be enabled by a user with administrative permissions. Once you've made your changes, click on the Save button.
With the feature enabled you'll be able to go to your Dashboard and use the RSS Feed button above Recent Campaigns. Clicking on the button will allow you to access the Recent Campaign RSS Feed URL and HTML options. Use the Copy button to copy the URLs or click the Dismiss button to close this window.