Then (1980's)                               Now (2020's)
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 - small Internet (thousands of hosts)      - huge Internet (billions)
 - computer = mainframe                     - computer = anything
 - timesharing, dialup, dumb terminals      - laptops, PCs, smartphones, WiFi
 - on 24x7                                  - transient connectivity
 - Unix, sendmail                           - diverse apps and OSes
 - SMTP and uucp                            - ESMTP (+ IMAP + POP + HTTPS)
 - delivery within hours                    - delivery within seconds
 - mail, elm, pine, alpine                  - Outlook, Webmail, Thunderbird
 - text-based ASCII                         - formatted text + attachments
 - plain text                               - encrypted and secure
 - open systems and standards               - closed proprietary systems
 - "good guys"                              - mix of "good guys" and "bad guys"