[ih] Design choices in SMTP

[Jack Haverty]

IMHO, the key to understanding the design decisions of SMTP is the "S".

Back in the mid 1970s, the ARPANET era, there was a lot of interest in 
using computers and networks to assist human-human communications.  
Professor Licklider, at MIT at the time, was a proponent of this both at 
MIT and during his tenure at ARPA.  I was one of Lick's students/staff 
and built one of the first mail systems.   RFC 713 documented a part of 
that system, as a piece of implementing Lick's vision, which included 
what we now know as email, forums, mailing lists, texting, social media, 
archival storage, notarization, workflow, user authentication, and other 
aspects of human-human communication.   The "Message-ID" field you still 
see today in email headers ("View Full Headers" to see it) was put into 
the header protocol as a part of that design, providing a "unique ID" 
for every piece of email sent, enabling them to someday be linked 
together in various kinds of relations - similar to how URLs now enable 
linking of web pages.

The system envisioned in Lick's "Galactic Network" was quite complex, 
and powerful, but deemed too big to implement for all the hosts on the 
ARPANET.  After much discussion and debate, mostly lost since it was 
done using email which was rarely archived at that time, a simplified 
first step was defined and documented by Sluizer and Postel (see 
https://www.rfc-editor.org/rfc/rfc772 and 
https://www.rfc-editor.org/rfc/rfc780 ).  This was MTP - the Message 
Transfer Protocol.

The mail system envisioned by 772 and 780 was also fairly complex and 
powerful, but also deemed too big as a "first step" for all hosts to 
implement.  Something else was needed, that could be easily and quickly 
implemented, to provide basic universal human-human communications over 
the ARPANET and the emerging Internet.

Something SIMPLE was needed -- and so the Simple Mail Transfer Protocol 
was defined and implemented everywhere as an interim solution.

So, IMHO, design decisions for SMTP were driven by Simplicity - the "S" 
in SMTP.

Seems like 40 years should be long enough.....maybe someone will take 
the next step.

Jack