free e-mail service offered by the American search engine company Google Inc. Google began offering Web-based e-mail accounts to select beta testers in 2004.

The e-mail service, rebranded as Gmail, was opened to the general public in 2007 and, when first launched, offered an unprecedented one gigabyte (one billion bytes) of free e-mail storage space, though users were also presented with advertisements based on keywords Google found in their messages. Google has regularly expanded the amount of free storage space given to users, which was in excess of seven gigabytes by 2008, and allows users to rent additional space. In 2007 Google acquired Postini, an e-mail security firm, for $625 million in order to improve Gmail's security, especially in Google's efforts to sign up businesses.

One of the main appeals of Gmail is that it is Web-based, so users can access their e-mail from any computer, personal digital assistant ( PDA), or “smartphone” connected to the Internet. Also, it gives users an e-mail address that is independent of any particular Internet service provider (ISP), which makes it easier to maintain a permanent address.