[kjellsbells]

I dont disagree with your criticisms of SMTP, but reading those early RFCs (eg 772) is a reminder of what a wildly different place the Internet was back then, and in that light, I feel it only fair to grant some grace.

MTP had one concern which was to get mail over to a host that stood a better chance of delivering it, where the total host pool was maybe a hundred nodes?

I speculate that Postel and Sluizer were aware of alternatives and rejected them in favor of things that were easily implemented on highly diverse, low powered hardware. Not everyone had IBM-grade budgets after all.

Alternative implementations of mail that did follow the kinds of precepts that you suggest existed at one time. X.400 is the obvious example. If I recall correctly, it did have rigorous protocol spec definitions, message length tags for every entity sent on the wire, bounds and limits on each PDU, the whole hog. It was also crushed by SMTP, and this was in the era when you needed to understand sendmail and its notoriously arcane config to do anything. So sometimes the technically worse solution just wins, and we are stuck with it.