Most prominent mail clients have built-in S/MIME support (Outlook, iOS, Thunderbird, Mail.app on macOS). The problem is that the there is no easy and free/cheap way to get an S/MIME certificate. My hope is that Let's Encrypt or Keybase or someone will make this easier someday.
S/MIME support has to be more widespread than just one or two providers with free certificates. Comodo's own iOS and Android instructions do not look straightforward at all.
Also, what happens when your certificate expires? Are you supposed to keep all expired certificates so you can still read older encrypted email? Does that even work?
