Anyway, there are some folks who credit other people, depending on context, but AFAIK Tomlinson gets it because, among other things, he was the guy who invented the use of the ‘@‘ to separate the user name and computer/domain names. Prior to that, messaging only worked if both the sender and recipient were working on the same computer.
Prior to that, messaging only worked if both the sender and recipient were working on the same computer.
Actually, you're also forgetting about the Internet "Bang Paths," when email was sent over the Internet using UUCP (pre-SMTP days.)
You needed to know the route the email message needed to take in order to get from your computer to the destination as well. It wasn't unusual for email routing messages to require being routed through as many as 10 different systems, and sometimes even more. Of course, that was way berfore the concepts of RFC821 and RFC822 (smtp messaging and smtp format records) and "mx" records in DNS simplified things tremendously.
There have been so many people who worked on Internet email it's really pretty staggering.
Mark