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Last year, Google kicked up Gmail with Priority Inbox, which uses a clever algorithm to decide which incoming email are most important to you. And now, with the introduction of Smart Labels, even more zero-config automated sorting is here to help your webmail woes.
Smart Labels will automatically scour for and tag any bulk mail, notifications, and forum communications you receive. You're not stuck with Google's default filtering rules either -- Smart Label rules can be customized to your taste just like those for any of your existing labels.
Smart Labels can be activated on your Labs page in Gmail -- just click that little green beaker in the top right corner.
More Info (http://gmailblog.blogspot.com/2011/03/new-in-gmail-labs-smart-labels.html)
source: Gmail Blog