The biggest problem of email is non verifiable routing due to header manipulation and lack of source authorization. If these were in place then it would be abl

The biggest problem of email is non verifiable routing due to header manipulation and lack of source authorization. If these were in place then it would be able to send all spam back to sender, instead of putting it a spam folder due to filtering, your email client just would send it back to the origin address. It also would help if each send would cost a token (of some monetary system) that would be returned on delivery at the legitimate destination. This would help against bulk sending. Email is a system that will always cripple at some point if there aren't real world cost incentives in place. People are the biggest problem with email, which is hard to solve with mere technical solutions.