I never said it was a program, it was one of the original protocols along with IP, FTP, TCP/IP, and GOPHER. All of these protocols described how the data was to be encoded into packets and transfered between different and seemingly incompatible computers
You may wish to check your post again. You said, quoting, "SMTP or Simple Mail Transfer Program."
Nor did GOPHER, FTP, or SMTP describe how data was to be encoded into packets, each relied on TCP for that. APRANET predated IP and TCP by several years, and it was possible to use BITNET without using any of the TCP-based protocols.
HTML was a much later protocol.
HTML is not a protocol at all. It's a language. Email formatted as HTML is transferred via SMTP. Web pages formatted as HTML are typically transmitted by HTTP.
SMTP also uses the much simple basic ASCII character set, only 12 characters, and produces much smaller messages. And sometime the smallest message possible is needed in certain situations.
Sorry, that's not true. The original specification for SMTP, RFC821, states "the mail data may contain any of the 128 ASCII character codes." The current SMTP protocol standard allows for, but does not require, an 8-bit transmission channel and these days most mail agents are in fact 8-bit clean.
If you want to photograph a man spinning, give some thought to why he spins. Understanding for a photographer is as important as the equipment he uses. - Margaret Bourke-White