To help people prioritize messages, Yahoo Mail will highlight the ones coming from senders who are in users' contact lists.

The enhancements are rolling out today in the U.S. and abroad in the coming weeks.

On the mobile front, Yahoo Mail's version for HTML mobile browsers will gain features previously available only on the desktop, such as the ability to download Microsoft Office documents, PDF files and photos. These new versions are available now on the iPhone's Safari browser.

Meanwhile, the beta of Yahoo Messenger version 10 is debuting Monday, with features like high-quality, full-screen video calls, an "updates" tab that notifies users of recent actions from friends, and a revamped "Insider" welcome page that can be customized by zip codes.

As Yahoo executives have said in the past, the company believes that social features are more useful when woven into the context of Yahoo services. This means Yahoo doesn't view social networking as a "destination" service, as it is in Facebook and MySpace.