Twenty years ago this week, on December 29, 1997, Bill Gates bought Microsoft a $450 million late Christmas present: a Sunnyvale-based outfit called Hotmail. With the buy—the largest all-cash Internet startup purchase of its day—Microsoft plunged into the nascent world of Web-based email. Originally launched in 1996 by Jack Smith and Sabeer Bhatia as "HoTMaiL" (referencing HTML, the language of th