It's a lot more fun that that, a single hop is barely 'routing' :) For bonus points Go back in history to when mail was literally routed hop by hop through SM

It's a lot more fun that that, a single hop is barely 'routing' :) For bonus points Go back in history to when mail was literally routed hop by hop through SMTP? How'd that work? What is the sending SMTP client expected to do when the server is unreachable? Have you seen the headers of a mail your receive on gmail? How many smtp hops inside gmails network? In an enterprise, how many smtp servers does your email hit before it exits? And that's partly how the horror of sendmail evolved :) Not even going into handling multiple email protocols and incompatible encoding types.