When Gmail launched on April 1, 2004, you could forgive established rivals Hotmail, Yahoo! Mail or AOL for seeing it as a bad April Fool's Day joke.

The trio had dominated free web email since the start of the 21^st century. Gmail started with a subscriber base of zero. What a difference a decade—and savvy marketing—makes, however.

Gmail today has anywhere from 289 million and 425 million subscribers worldwide. It's the biggest free web email service (some claim it's the third largest). But the question you should be asking are where's Hotmail, Yahoo! Mail and AOL today? Your silence speaks volumes.

When Google launched Gmail a decade ago, it saw the service was it's way of making email better. Insiders later revealed that Gmail was the product of an engineer's 20 percent free time.

But Google co-founder Larry Page explained that Gmail was a response to an email from a frustrated Google fan who complained loudly of the service limits imposed by Hotmail, Yahoo! Mail and AOL.

Gmail responded with one gigabyte of storage, removing the need for a user to constantly prune his inbox to stay under the provider's limit. Microsoft's limit was a just 250 MB. Neither did Google deactivate an account following period of inactivity as Microsoft did.

Gmail also offered better features in more areas that its rivals were forced to adopt. These features included spam filtering and message threading. Gmail was also mobile-ready from the start and worked in most browsers by default.

Two months after Gmail launched, Microsoft increased the Hotmail inbox from 2 MB to 250 MB but kept charging for extra storage.