The reason why I need something like Mailpile (and the problem they will hopefully solve) is to have a client-side app with a user-friendly system for managing

The reason why I need something like Mailpile (and the problem they will hopefully solve) is to have a client-side app with a user-friendly system for managing S/MIME certificates. I can set up the CA and generate user (employee) certificates on my own, there's no way the end-user should have to do that. But what's frustrating right now is that the current tools for configuring S/MIME signing and encryption for email either (a) don't exist, or (b) are heinously complicated to use. Have you ever tried getting S/MIME certificate auth set up in Mac Mail? It's doable but I had difficulty walking my tech-savvy brother through the process over the phone. If Mailpile has a simple method of selecting a certificate file for an email account then the hard part is done IMO. The process just becomes IT issuing new certificates every year to employees, and employees uploading said certificates through their (web) mail app. The biggest value here is having a web mail client, hosted locally, that can support PGP/SMIME in a user friendly way. Then signed/encrypted emails are that much easier to configure for the masses.