The man who invented the email, Mr Ray Tomlinson, has died of a suspected heart attack at age 74.
The New York-born American computer programmer discovered in 1971 that electronic messages could be sent across different computer networks.
Tomlinson is suspected to have died of a heart attack on Saturday, according to a report by the BBC.
He sent the first email ever delivered worldwide while working at research firm Bolt, Beranek and Newman (now BBN Technologies) in Boston.
“Thank you, Ray Tomlinson, for inventing email and putting the @ sign on the map. #RIP,” said Gmail on its Twitter page.
Other comments on the late Tomlinson include one from the US TV morning show "Good Morning America", which tweeted: “RIP inventor of modern email Ray Tomlinson, who helped change how we communicate.”
The firm where Tomlinson worked played a big role in developing an early version of the Internet, called Arpanet.
Reports by the BBC say that Tomlinson later said he could not remember what was in that first test message, describing it as “completely forgettable”.
In a 2009 interview, Tomlinson described the first email thus: “Every time you test you have to generate some sort of message. You might drag your fingers across the keyboard or just type the opening phrase from Lincoln’s Gettysburg address or something else — so technically the first email is completely forgettable and therefore forgotten.”