The spam filtering in Google’s Gmail email service has long been praised by its users. Last week Google added a new feature likely to be similarly popular that will also earn the company some new enemies: filtering of bacn–the automated notifications, marketing messages and newsletters that clog many an inbox.

The new design splits a user’s inbox into five separate tabs. The default view, Primary, shows only email conversations with other people. You have to click tabs to access the other four: “Social” is for notifications from social networks and personal emails sent to many recipients; “Promotions” contains marketing emails such as offers from online stores; “Updates” houses billing statements and the like; “Forums” is for discussion-site messages and mailing lists.

When I turned on the new inbox (see how to do that here) I immediately liked it. The default view that shows only emails from other humans is an improvement over my previous inbox. which jumbled those messages with various newsletters and notifications that, although I had opted into them, I mostly never read and didn’t want to see. It quickly became clear that if I never click the “Promotions” tab, all that bacn will essentially disappear without requiring me to unsubscribe from each mailing list.

For that reason, I suspect that Gmail’s new design will be popular with its users, and perhaps convince some people to switch to the service. That means a lot of bacn email being filtered out, which has the potential to be quite a headache for companies that rely on email marketing (as well as politicians seeking office and hoping to emulate last year’s Obama campaign; see “A More Perfect Union”). It would be interesting to know, a few months from now, if there has been a measurable drop in users opening these kinds of messages.

Social networks such as Twitter and Facebook may feel the effects, too. They rely heavily on email to pull people back into their services (Twitter is particularly aggressive in using emails, in my experience) and the new Gmail means those messages won’t reach a person unless they click over to the “Social” inbox tab. Worse, from the perspective of social networks, while their emails get hidden, notifications for Google’s own social network appear in a red box in the top-right corner of every Gmail inbox.