Google co-founders Larry Page and Sergey Brin loved pulling pranks, so much so they began rolling outlandish ideas every April Fools’ Day not long after starting their company more than a quarter century ago. One year, Google posted a job opening for a Copernicus research center on the moon. Another year, the company said it planned to roll out a “scratch and sniff” feature on its search engine.

The jokes were so consistently over-the-top that people learned to laugh them off as another example of Google mischief. And that’s why Page and Brin decided to unveil something no one would believe was possible 20 years ago on April Fools’ Day.

It was Gmail, a free service boasting 1 gigabyte of storage per account, an amount that sounds almost pedestrian in an age of one-terabyte iPhones. But it sounded like a preposterous amount of email capacity back then, enough to store about 13,500 emails before running out of space compared to just 30 to 60 emails in the then-leading webmail services run by Yahoo and Microsoft. That translated into 250 to 500 times more email storage space.

Besides the quantum leap in storage, Gmail also came equipped with Google’s search technology so users could quickly retrieve a tidbit from an old email, photo or other personal information stored on the service. It also automatically threaded together a string of communications about the same topic so everything flowed together as if it was a single conversation.

“The original pitch we put together was all about the three ‘S’s” — storage, search and speed,” said former Google executive Marissa Mayer, who helped design Gmail and other company products before later becoming Yahoo’s CEO.

It was such a mind-bending concept that shortly after The Associated Press published a story about Gmail late on the afternoon of April Fools’ 2004, readers began calling and emailing to inform the news agency it had been duped by Google’s pranksters.

“That was part of the charm, making a product that people won’t believe is real. It kind of changed people’s perceptions about the kinds of applications that were possible within a web browser,” former Google engineer Paul Buchheit recalled during a recent AP interview about his efforts to build Gmail.

It took three years to do as part of a project called “Caribou” — a reference to a running gag in the Dilbert comic strip. “There was something sort of absurd about the name Caribou, it just made make me laugh,” said Buchheit, the 23rd employee hired at a company that now employs more than 180,000 people.

The AP knew Google wasn’t joking about Gmail because an AP reporter had been abruptly asked to come down from San Francisco to the company’s Mountain View, California, headquarters to see something that would make the trip worthwhile.

After arriving at a still-developing corporate campus that would soon blossom into what became known as the “Googleplex,” the AP reporter was ushered into a small office where Page was wearing an impish grin while sitting in front of his laptop computer.