STARTTLS Everywhere
This is far too little, too late:* The SMTP RFC says that mail servers MUST NOT require STARTTLS to receive mail. Postfix (and I imagine most other production grade SMTP servers) has an option to require STARTTLS anyway, so if you really want STARTTLS you can already require that clients have it enabled, despite the braindead standard.* STARTTLS ensures that mail was encrypted only in the final hop, from the last server to your server. That usually means it transited the public internet encrypted, but it definitely does not assure it.There are interesting email security efforts afoot, notably the draft standard called "SMTP Require TLS": https://tools.ietf.org/html/draft-ietf-uta-smtp-require-tls-... . Unfortunately the reality is that the internet mail infrastructure evolves at an incredibly glacial pace. The entire SMTP protocol would benefit greatly from the adoption of an SMTP/2 protocol, rethought with modern security practices in mind.