How Big Was ARPANET?
Tomlinson’s Idea. “The idea occurred to me that CYPNET could append material to a mailbox file as readily as SNDMSG could.” As CYPNET was originally written, it could send and receive but could not change or add to a file. Tomlinson adapted CYPNET to use SNDMSG to deliver messages to mailboxes on remote machines, through the ARPANET.