This tutorial provides the steps required to add RSS feed in Mail App on Mac OS X Lion system. You can add a new RSS feed using the option available as part of File menu.
Launch Mail app and click the File menu. Select Add RSS Feeds from the displayed menu list.
In the following Add RSS Feeds window select Specify the URL for a feed and enter the feed URL in the text below.
If you want to read the RSS feed articles in your Inbox then mark the check box with label as Show in Inbox. After making the necessary changes, click the Add button. Now the RSS articles from the configured blog or website will be displayed in Inbox as well as under RSS section.