RocketMail was one of the first major, free webmail services. The service was originally a product of Four11 Corporation. For a brief time, RocketMail battled with Hotmail

Hotmail

Windows Live Hotmail, formerly known as MSN Hotmail and commonly referred to simply as Hotmail, is a free web-based email service operated by Microsoft as part of its Windows Live group. It was founded by Sabeer Bhatia and Jack Smith and launched in July 1996 as "HoTMaiL". It was one of the first...

 for the number-one spot among free webmail services. Four11, including RocketMail, was acquired by Yahoo!

Yahoo!

Yahoo! Inc. is an American multinational internet corporation headquartered in Sunnyvale, California, United States. The company is perhaps best known for its web portal, search engine , Yahoo! Directory, Yahoo! Mail, Yahoo! News, Yahoo! Groups, Yahoo! Answers, advertising, online mapping ,...

 in 1997. Yahoo! assimilated the RocketMail engine. Yahoo! Mail

Yahoo! Mail

Yahoo! Mail is a web mail service provided by Yahoo!. It was inaugurated in 1997, and, according to comScore, Yahoo! Mail was the second largest web-based email service with 273.1 million users as of November 2010....

is essentially the old RocketMail Webmail system.

At the time of the transition, RocketMail users could either choose a Yahoo! ID, since they were not guaranteed the availability of their RocketMail ID on Yahoo!, or could use username.rm as their Yahoo! ID.