I was looking into some more secure emailing protocols and I found some opensource ones. The only thing is, I am not sure how fast they are because I have not seen much testing. If you wanna check them out yourself they are called DMTP (Dark Mail Transfer Protocol) and DMAP (Dark Mail Access Protocol). These were made by the founder of an encrypted emailing service Lavabit under the name The Dark Mail Technical Alliance. I hope to look into all of these, including JMAP very soon. Thanks for the suggestion!