When Gmail was released to the public on April 1, 2004, many people thought it was a prank. Gmail offered one gigabyte of storage and robust email search. These features, among others, have helped to make Gmail the most used email service in the world with 1.5 billion users. Gmail has come a long way since its inception. It stands as the most dominant online email service with more than 1.5 billion global active users. It has gone from a small experiment to an important piece of Google’s G Suite lineup. But the road to the top hasn’t been without a few bumps, including a rocky start. By the time Google started working on the service in 1999, Yahoo Mail already had 12 million active users and Microsoft’s Hotmail had about 30 million. CNBC News video.