At 12 PDT today Yahoo will for the first time start offering free e-mail accounts under two new domains: ymail and rocketmail. Both ymail.com and rocketmail.com already lead to the Yahoo Mail landing page; if you register your free e-mail account under one of these two new domain names, you'll get the exact same features as you would with "standard" mail.yahoo.com.
Experienced surfers (that's a nice way to say "old") will recognize Rocketmail as one of the first free e-mail services around, acquired by Yahoo (along with its owner, Four11) back in 1997. Other than for nostalgic reasons, I doubt many surfers will run to register their [email protected] accounts; the domain name is a bit too long for today's standards.
Ymail, on the other hand, is a clear jab at Gmail. Although Yahoo Mail is the market leader with the most users (266 million worldwide in April), Google caused a major disruption when they offered nearly unlimited storage capacity. That, along with the fact that Gmail was great at killing spam and really easy to use, was enough to grab a big piece of the free e-mail market - 101 million users in April, according to the AP. Yahoo and Microsoft have, for the most part, caught up with Gmail's storage offering - Yahoo Mail now offers unlimited storage - but Gmail is now killing them with features and great integration with other Google services.