In April 2004, Google launched GMail as invite-only and introduced one of the biggest (if not the biggest) Inbox in all of the free email world. The default storage size of the inbox was 1GB and increases algorithmically everyday.
Here’s an infographic of the Evolution of GMail, outlining the development of one of Google’s most widely used services. With 1GB right out of the inbox, it was among the biggest with other existing services only giving 50MB to 250MB back then.
Before GMail, most people were either using Yahoo!, HotMail and other similar services. GMail practically stole the limelight in free email and is now among the top 3 email services in the world.