To use the feature, users would need to be logged in to their Google account and the Gmail results would be visible only to them.

The feature is an attempt by Google to make its search results "truly universal," because answers to certain queries may be contained in users' Gmail messages, the company on Wednesday.

"So if you're planning a biking trip to Tahoe, you might see relevant emails from friends about the best bike trails, or great places to eat on the right hand side of the results page. If it looks relevant you can then expand the box to read the emails," Amit Singhal, senior vice president of search at Google, wrote in a blog post.

Google already offers signed-in users the option to mesh personal results with links to public Web pages, an initiative it calls Search Plus Your World.

People who allow Google to personalize their search results see, for example, relevant posts authored by their Google+ contacts, photos from their Picasa albums and links from their Reader syndicated feed manager. If users also let Google log their Web usage via the Web History feature, that data is also used to tailor search results.