title: How to set up a bidirectionally encrypted email server?
body: <p><strong>Encrypted email - sounds like a great thing, right?</strong> Problem already solved, right? Well... I don't think so and I'm hoping I'm wrong!</p>
  
  <p>To understand what I'm asking, <strong>please understand what I'm NOT asking</strong>: I am not asking how I encrypt and sign messages sent over public networks. This is a bit different.</p>
  
  <p>I want to set up a mail server where email clients can both read and post and their messages to the mail server encrypted in both directions, preferably using standard clients available at internet cafes, etc, without requirement for specialized software or encrypted port-forwarding a-la SSH. </p>
  
  <p>The key here is that there is a trusted mail server which can deliver email to a community using a local-delivery-agent. One can then send email to and receive from anyone and everyone who also uses that same system without concern for the security of their communications. There's no need to encrypt every message using the public key of every recipient - what pain THAT would be! - and instead all we're talking about here is a bidirectional communication that's encrypted from clients to this system.</p>
  
  <p>Of course, public messages come in unencrypted via the usual port 25 process to all participants of the email server. They may or may not be encrypted as they were - we're not worried about them. Email Clients connect from anywhere and the responding code on the server system encrypts those messages for reading, even though they were sent through the public network in plain text already... <strong>This much I can already get fairly easily with encrypting IMAP servers like Dovecot.</strong></p>
  
  <p><strong>What I want to add to this is that connected email clients can <em>send</em> email, encrypted, back to the system of which they are a client</strong> wherein that system forwards externally unencrypted, wherever it needs to go. If it's a local mailbox, the message is delivered via a local delivery agent. No keys involved there. The advantage of this design is that there's NO exposure of the email to external, untrusted systems or networks, and if the delivery is local, it's effectively protected end-to-end WITHOUT having a point-to-point hassle of encrypting individual messages in the more typical use.</p>
  
  <p>This would be "god send" because as it is now, it's impossible to send secured mail through clients on the public internet to groups of people within an internal network.</p>
  
  <p><strong>I guess another way to phrase what I’m asking for is: Has someone created a package that gives us the other half of the encryption that IMAP (and POP?) servers already do – that distant clients on untrusted networks can hand-off out-bound unencrypted email through an encrypted link to the server on the other end?</strong></p>
  
  <p>ANOTHER ALTERNATIVE occurred to me: Encrypting SMTP / ESMTP servers that talk mail server to mail server in an encrypted form. (Similarly, clients should be able to hand off unencrypted email through an encrypted link, much as https works.) Anybody know of such a package? This is not quite as good, but an important part of email architecture...</p>
  
  <p><strong><em>If this doesn’t exist today, it should!</em></strong></p>
  
  <p>Thanks for your thoughts, pointers, etc.</p>