Yahoo Inc. is offering free e-mail accounts under two new designations in an effort to attract Web surfers unhappy with their current addresses.

The Sunnyvale-based company expects to begin registering new addresses under the domains of "ymail" and "rocketmail" around noon PDT Thursday at http://mail.yahoo.com.

It will be the first time that Yahoo has offered e-mail accounts under umbrellas other than its own company name since it became a correspondence conduit in 1997.

Yahoo began offering free e-mail shortly after its $80 million acquisition of Four11 Corp., which included the rocketmail domain. Rocketmail users at the time of the acquisition were allowed to keep their existing accounts, but Yahoo hadn't accepted any new addresses under that name until now.

The diversification into new e-mail designations is being driven by the difficulty that people are having as they try to find an appealing e-mail handle under the Yahoo domain.

Most people prefer an e-mail address that's easy to remember - like the first letter of their first name in front of their last name - or reflective of a personal interest, like a hobby or favorite sports team.

But the popularity of Yahoo e-mail had narrowed the range of choices, forcing users to perform too many mental gymnastics to come up with an e-mail handle that hadn't already been taken.

"We realized we needed to expand the universe of Yahoo mail," said John Kremer, a vice president in charge of Yahoo's e-mail.

Yahoo is hoping the additional options created with the ymail and rocketmail will help boost its e-mail growth. Although it's given away, e-mail is considered an important product because it fosters user loyalty and spurs frequent visits that create advertising opportunities.

With 266 million worldwide users in April, Yahoo is the e-mail market leader, according to the latest data from research firm comScore Inc. Microsoft Corp., which unsuccessfully tried to buy Yahoo for $47.5 billion, is a close second at 264 million users.

But e-mail accounts at both Yahoo and Microsoft have been growing at a slower pace than Google Inc.'s Gmail, which has added more than 30 million users in the past year. About 101 people used the Internet search leader's Gmail in April, comScore said.

E-mail under the ymail and rocketmail designations will offer all the same features as the Yahoo domain, including an unlimited amount of storage capacity.

When it entered the e-mail market, Yahoo provided just 3 megabytes of free storage per account. But Google changed the competitive landscape in 2004 when it introduced gmail with 1 gigabyte of free storage under its Gmail service. Gmail now offers more than 6 gigabytes of free storage.