WIP: Mozilla SSL

• do dovecot (see GitHub PR on https://github.com/mozilla/ssl-config-generator/)
• for server-to-server SMTP, we'll probably have to tolerate older crypto etc.
  • should we even risk allowing the user to fiddle with it?
  • if a client can't negotiate SSL, do they fall back to cleartext, or does delivery fail?
• upstream the postfix dhparam stuff?
• testing. upgrading postfix's openssl seems a big step, but maybe not.
• do we need to generate non-RSA keys?
• send a patch to postfix http://www.postfix.org/lists.html to allow setting ciphersuites
• dovecot ciphersuites patch
• dovecot tlsv1.3 min patch
• postfix: smtp_tls_* as well as smtpd_tls_* (upstream to Mozilla conf?)