Edison&#x27;s first profitable invention, in 1869, was a way to get stock tickers to sync up automatically. It was a hack (send lots of idles every once in a while to force the printing wheel to hit a stop) but it was good enough to deploy.  Previous printing telegraph technology, back to 1852, required a skilled operator at the receiving end to manually sync. That was used only for main lines with heavy traffic.<p>Howard Krum finally figured out how to do sync right in 1919, when he invented serial stop-start async as we know it today.  In 1924, he came out with the Teletype Model 14 tape printer, with the first reliable mechanical async decoder. That design was used into the 1960s, and most computer serial ports are compatible with it.  (45.45 baud, 5 bits, no parity, 1.5 stop bits.)<p>Telegraphy was store and forward, but manual at first. By the late 1920s, punched tape was used, but someone had to manually look at tape, tear off each message, and put it in the proper outgoing reader.  This was manual Sendmail.  After WWII, automated forwarding centers were built, with paper tape punches connected to readers via a bin as the storage mechanism and telephone-like switches to change connections. These were hugely expensive to operate for the amount of data transferred, but it was essentially email, with electromechanical technology.<p>(I restore Teletypes as a hobby.  Here&#x27;s a Model 14 working.[1]. If you want to see some in action, they&#x27;ll be at the Clockwork Alchemy Steampunk Convention, Memorial Day weekend, in San Jose.)<p>[1] <a href="https:&#x2F;&#x2F;archive.org&#x2F;details&#x2F;Aethericmachine14" rel="nofollow">https:&#x2F;&#x2F;archive.org&#x2F;details&#x2F;Aethericmachine14</a>