Username or EmailPassword
"TLS does have a role in e-mail, and it's not encryption. TLS provides authentication. Authentication is arguably the largest problem with e-mail."
I agree that this is one of email's bigger problems, and though there are solutions, the fact that we cannot depend on them working even a fraction of the time make them somewhat useless. What good is authentication if it doesn't work reliably with my current contacts? If we allow any exceptions for others to contact us without authentication, then email remains vulnerable. I doubt we'll see a massive roll out to fix SMTP's problems. We're more likely to see people adopt a new service that has security built into it from version 1.
"The original protocol simply trusted clients and servers not to lie about who they were, and that's why we have spam. If our servers only accept mail from servers authenticated with certificates, then blocking spam is easy."
I disagree, authentication won't stop spam. Spam will just be authenticated like any other mail. Not all spammers use forged headers.