Mozilla released Thunderbird V1.0, which is now available at their web site:
http://www.mozilla.org/products/thunderbird/
This is a great open source free email program which now includes RSS feed client. It is a good replacement for Microsoft Outlook Express, and for many of us, a good replacement for Microsoft Outlook that comes with Microsoft Office.
It has many features but there are still some lacking. Even as an RSS client, it should have a few more features added to allow you to specify the frequency of refreshing a feed along with a form of aggregation, so that when you click on a folder, it will display a list of all the entries for all feeds in the folder or nested under the folder. Currently, it appears, you would have to click on each feed to read them.
When you have multiple email accounts, it builds an entry for each with an inbox, drafts, templates, sent and trash folders. You can combind them into one folder, but it would be hard to track which message came from which account. My main grip is that you have to leave these groups expanded so that all the sub-folders show to know when new mail arrives in the folder. It does not have the count of unread emails shown on accounts that are collapsed, so you would have to expand the group to know if there is any mail. For many this will probably not matter much, but if you are like me and have many accounts (I have over 30 to watch over), this makes for a lot of scrolling to see find the new mail.
Overall though, it is a quality program which I recommed for the email functionality. The RSS still needs to be improved before I will get rid of ShaperReader.
Also note, if you already use a prior version of Thunderbird, most of your extentions will probably not work.