You can also type the word “Gmail” into the search box and Google will include those results in the main column under the assumption that you’re more interested in those results compared to others.
While your inbox houses a lot of useful personal information, and it could simplify your digital life to have everything unified under one account, it could raise security concerns for many. If you’re not interested in personalized results, you can click an icon that hides them. Right now, this is also how you turn off personal search results from Google+ — something Google will hopefully remedy in future iterations.
The field trial is limited, but you can sign up for early access. According to Google, it will take “a couple of months” to get your account activated.