Yahoo has begun testing new version of its Web mail service with a new user interface that works more like a typical desktop email application.

The beta version of the new Yahoo Mail will be made available to an undisclosed number of US users, and to more users in the coming months Yahoo said.

The company isn't providing an estimate for when the new service will fully launch, but the idea isn't to have a prolonged beta period, said Ethan Diamond, director of product management for Yahoo Mail. "We want to make the beta as short as possible," he said.

Users for whom the beta is made available will be able to toggle between the new Yahoo Mail and the current version, and changes they make on either version will be automatically reflected on the other, Diamond said.

The new service is based on technology Yahoo acquired when it bought Oddpost in July 2004 and requires only that users access it with either Internet Explorer or Firefox, Diamond said. No additional software is required, he said.

The new Yahoo Mail offers user interface features that have been common for many years in email desktop applications, including the ability to drag-and-drop messages into folders, a pane to preview messages' content, the ability to have multiple message windows open and keyboard shortcuts to, for example, delete or create messages.

Other features include an advanced search feature for searching through headers, attachment content and message bodies, and the ability to scroll through all messages in a folder instead of having a folder's messages split up among multiple pages the user needs to move through, Diamond said.

Yahoo will also progressively add other features. The new service will be free in its basic form, with a fee-based option that offers more storage and some additional features.

The improved Yahoo Mail reflects Yahoo's realization that Web mail services have evolved from simple personal mailboxes into information management applications that people are using to store and organize content such as digital songs, photos, video and content syndication feeds, said Allen Weiner, a Gartner analyst.

"In essence Yahoo realized that the format or application of its current mail product wasn't suitable as a real content management vehicle," he said. "It's a very dramatic step when you change [to this extent] the metaphor of your Web mail service."

Weiner sees a big potential for Yahoo to add significantly advanced features on top of the initial set that debuts with the beta version. For example, it would make a lot of sense for Yahoo to add features for accessing and managing content syndication feeds into Yahoo Mail, he said. "I think a lot of what is important about it is not necessarily what we're seeing [today] but what's most likely to come," Weiner said.