Before Tomlinson invented direct electronic messages between users on different machines on a certain network in 1971. Before then, users could only write messages to others using the same computer.
"A true technology pioneer, Ray was the man who brought us email in the early days of networked computers," his employer, Raytheon, said in a statement.
"His work changed the way the world communicates and yet, for all his accomplishments, he remained humble, kind and generous with his time and talents, He will be missed by one and all."
A company spokesman said Tomlinson passed away on Saturday, and the cause of death was not yet confirmed.
Tributes poured in from the online world.
"Thank you, Ray Tomlinson, for inventing email and putting the @ sign on the map. #RIP," Google's Gmail team tweeted.
Vint Cerf, considered one of the fathers of the Internet who was once a manager of the US Defence Advanced Research Projects Agency (DARPA), lamented the "very sad news" of Tomlinson's passing.
When Tomlinson invented the user@host standard for email addresses, it was applied at DARPA's ARPANET, the Internet's precursor. He was the first to use the @ symbol in this way, to distinguish a user from its host.
The Massachusetts Institute of Technology graduate detailed his creation on his blog, in an attempt to prevent legend from overtaking the facts.
"The first message was sent between two machines that were literally side by side" connected only through ARPANET, he wrote on his blog.
"I sent a number of test messages to myself from one machine to the other. The test messages were entirely forgettable and I have, therefore, forgotten them.
"Most likely the first message was QWERTYUIOP or something similar," he added, referring to the first letters on the traditional English-language keyboard.
"When I was satisfied that the program seemed to work, I sent a message to the rest of my group explaining how to send messages over the network. The first use of network email announced its own existence.