In November Gmail briefly introduced Syndication of one's email inbox. This has now been made widely available.
You can view Gmail messages in your aggregator by subscribing to a new channel. Enter https://gmail.google.com/gmail/feed/atom in the ‘URL’ field, and submit your Gmail address and password.
Please keep in mind that Gmail messages don't appear in your aggregator unless there are unread messages in your inbox.
There's some security risk here. If you use a web based RSS client, like Bloglines, your email pw is available to anyone that hacks Bloglines. Safest for a local RSS client. In fact, at the moment, Bloglines doesn't support this feed. It does work in Firefox though (go to bookmarks, from bookmarks menu choose live bookmark, enter url. It displays in Bookmarks drop down menu as a folder in which each inbox item shows up as a bookmark.).