You've more-or-less described DKIM. You can see some issues with it here: https://en.wikipedia.org/wiki/DomainKeys_Identified_Mail#Weaknesses https://en.wikiped

You've more-or-less described DKIM. You can see some issues with it here: https://en.wikipedia.org/wiki/DomainKeys_Identified_Mail#Weaknesses https://en.wikipedia.org/wiki/DomainKeys_Identified_Mail#Wea...