Yahoo, which already allows users to search emails in their Yahoo accounts, began testing enhanced email search Tuesday in what analysts said is part of an effort to stop users from defecting to Google's Gmail, reports Red Herring. Yahoo email users will now be able to search all of their email attachments, including photos, which account for 40 or so percent of Yahoo attachments.

The announcement comes a week after Google upgraded its Desktop search to index users' Gmail and Microsoft Outlook email accounts while also searching their hard drives and web search histories, points out the International Herald Tribune.

The need to search emails is a result of the expanded storage capacity of email systems, prompted by Gmail, which offers two gigabytes of storage at no cost. Yahoo offers one gigabyte for free - and two gigabytes for an annual fee.

Enhanced email search is just one part of Yahoo's plan, according to JupiterResearch analyst Gary Stein.

"Their big challenge is to get you to save everything on email—all your photos, videos, and everything you want to share—and ultimately solidify your relationship with them," he is quoted by Red Herring as saying. More users potentially means more advertising dollars, and Yahoo plans to roll out several email improvements in the next few months.

The search enhancements also include categorized search results - broken down into senders, folders, attachments, message status, and date - as well as quick photo and attachment views, according to a post in the SearchEngineWatch blog.

Yahoo's email is the most widely used service in the U.S., with some 167 million users, according to comScore, while Gmail, which is officially still in beta, has only 5.4 million users - and Yahoo would like to keep those number that small. America Online has nearly 49 million, and MSN Hotmail has more than 44 million.