&gt; spam detection, access, standardization and inter-operability<p>Spam detection works on a higher level than transport security, it is independent from transport (although a spam classifier might favor mails from SMTP servers sent with SSL and a client certificate signed by a CA for its domain name).<p>Access... well, that&#x27;s IMAP&#x2F;POP3&#x27;s job, both support SSL for ages.<p>Standardization&#x2F;interop, uh we already have SMTPS. The standard is there, what&#x27;s lacking is support for inter-server encryption.