Tomlinson was one of group of scientist who were working on developing better computer. the scientist at his site were able to send a message to a "mailbox" on the computer on their site. other scientist could view the messages in the mailbox. but there were other computer at other sites where scientist were working on the same project. Tomlinson's idea was to figure out a way to deliver messages to mailboxes on those remote computers. he used the @ sign to identify messages that were headed out of the local machine to the more distant ones. that was the start of the email systems that we still use today.