We rely so much on email, and yet it's still largely a blackbox. We type into the box and hope the other side gets our message. Amazing how so much has changed on the Internet, and yet so little has changed.
The notebook pictured below is the IMP Log from Professor Leonard Kleinrock's lab at UCLA. The IMP log documents the first message that went out over ARPANET on October 29, 1969. ARPANET is the predecessor to what we know now as the Internet.
I had the pleasure of attending the 35th Anniversary of the Internet at UCLA and listening to Professor Kleinrock talk about that October day in 1969 when the letters L and O were transmitted from UCLA. LO was the first message sent out over ARPANET, the system crashed before the other side received the full message: "LOGIN".
A telephone headset was mounted on the programmers at both ends so they could communicate by voice as the message was transmitted. At the UCLA end, they typed in the "l" and asked SRI if they received it; "got the l" came the voice reply. UCLA typed in the "o", asked if they got it, and received "got the o". UCLA then typed in the "g" and the darned system CRASHED! Quite a beginning. On the second attempt, it worked fine!
Over 40 years later, we are still having to manually confirm if the other side got our message.