Just to defend Dr. Percival a little here(since I have the same stance, though we do also support TLS), the RFC's require you to support non-encrypted SMTP. Si

Just to defend Dr. Percival a little here(since I have the same stance, though we do also support TLS), the RFC's require you to support non-encrypted SMTP. Since you HAVE to support it(not only per RFC but because in the real world so many SMTP communicators are stupid, lazy, or ignorant), there is little point in trying to make email secure. Until such time as everyone decides TLS1.3+ is required for SMTP, there is no hope, so why bother. Our external auditors get all upset about it every single year, and every single year, I show them the RFC's and they then shutup about it for a year. If you feel strongly enough about it, try to get a RFC passed where SMTP requires TLS now.