An RFC would be interesting, but I am not sure it would be adopted. You might start with a gist on github with the configuration settings required to do this i

An RFC would be interesting, but I am not sure it would be adopted. You might start with a gist on github with the configuration settings required to do this in postfix, qmail, sendmail, powermta, etc. It might help to give the page a shiny logo and a trendy name. If there is enough interest, perhaps even register a domain with a catchy name. What would be a good name for it?