howto be your own s/mime key master for sending and receiving s/mime signed and encrypted mails, a public certificate authority is not necessary. here is how you manage to be your own s/mime key and certificate master. this
howto how to set up s/mime on iphone and mac update (may 28th, 2016): this article is slightly outdated. please read these instructions instead s/mime (with sha2 encryption) is currently the best way to send signed and end-to-end encrypted mails. it is