Today, Gmail turns 20 years old. It was April 1, 2004, when Google put out its famous press release announcing that it was releasing its email service to beta users. You’ve probably read about how, at the time, most people thought it was an April Fool’s Day joke. I mean, it did seem pretty preposterous that Google was making an email service that gave users 1GB of storage. That was an astronomical amount at a time when most services limited you to a few megabytes.

You may also have heard about how Gmail originated as a “20 percent project.” Basically, Google requires engineers to spend one day a week working on a project that isn’t their job. They are side projects. Of course, in addition to Gmail, several of Google’s most important products came from these side projects, like Google Maps and AdSense. 

At the time, search was the second-most popular thing people did on the internet. Email was the first. It makes sense, then, that Google, a company whose primary business is a search engine, might be interested in what it could do about the only thing people spend more time doing online. 

The most interesting thing about the entire thing was that it almost wasn’t. According to the original press release–the one everyone thought was a joke–the entire idea originated with a user complaint. 

The inspiration for Gmail came from a Google user complaining about the poor quality of existing email services, recalled Larry Page, Google co-founder and president, products. “She kvetched about spending all her time filing messages or trying to find them,” Page said. “And when she’s not doing that, she has to delete email like crazy to stay under the obligatory four megabyte limit. So she asked, ‘Can’t you people fix this?'”

From there, an engineer took on the challenge of building an email service that solved the three biggest problems: storage, speed, and search. It makes sense that Google would build an email service that made it easier to organize and search for messages. It does know a thing or two about search. 

The storage thing was just crazy and was what–more than anything else–made people think it was a joke. Giving away 1GB of storage was just unbelievable in a world where your inbox might allow you to have 15MB of messages and attachments. As a result, most people had to regularly delete messages just to stay under their limit, or risk not receiving new emails. 

Google’s solution was that you’d never have to delete an email message ever again. Oh, and it was free–which was a huge deal considering almost every other email service charged money for a tiny fraction of the storage and few other features at all. 

I think it’s fair to say that Google solved the problems most people faced with email at the time. Gmail represented a sea change from what came before it, and along the way became the most popular email service on the planet, with more than 1.5 billion users. 

“If a Google user has a problem with email, well, so do we,” said Google co-founder and president of technology Sergey Brin at the time. “And while developing Gmail was a bit more complicated than we anticipated, we’re pleased to be able to offer it to the user who asked for it.”

There is an obvious lesson here, which is that often the very best products are the ones you make in direct response to a customer’s problem. You can have all the product road maps you want, but nothing beats listening to what your customers say their real problems are and finding ways to solve them that your competition won’t. 

That’s really what happened here. A Google user had a complaint, and the company realized it could solve it in a way that no other email service was willing to. No one else was willing to give away that much storage. No one else was building better search and organization. Certainly, no one else was giving it away for free. It makes you wonder what other 1.5 billion user ideas might be out there waiting for someone to listen and say, “Hey, we could fix that.”