The new domains are "ymail" and "rocketmail." To establish a new email address, go to http://mail.yahoo.com.
According to the Associated Press,
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 . . .
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.