Regarding headers, here's an example of a full email source sent from my ProtonMail account to a non-ProtonMail account unencrypted...
Code:
Return-path: <redacted>
Envelope-to: <redacted>
Delivery-date: Fri, 16 May 2014 10:51:12 -0700
Received: from mail.protonmail.ch ([37.35.106.36]:40023)
by whub39.webhostinghub.com with esmtps (TLSv1:DHE-RSA-AES256-SHA:256)
(Exim 4.82)
(envelope-from <redacted>)
id 1WlMHo-0006Py-Ky
for <redacted>; Fri, 16 May 2014 10:51:12 -0700
Received: by mail.protonmail.ch (Postfix, from userid <redacted>)
id 8412E14250641; Fri, 16 May 2014 17:50:52 +0000 (UTC)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=protonmail.ch;
s=default; t=1400262652;
bh=5XJEnonlaxIM0My6t8LmMrweIrr1YWD4ZknMfuXae6o=;
h=To:Subject:Date:From:Reply-To;
b=bF9uuVO4U8fOFo+nGn4CHyll5k9kzLLDCScwPcZlkWfn924rSzJk219lD32toaC3b
T0bQwcTDB6JEqeYPLLf1NY/79w0tIfxhOxYiIKlgH56gtwB74j0kgPnO23k0pnTJ10
rvW3AK/4PGrJG5u0HtNBvVO6GFvkpliwH8sq/wsI=
To: <redacted>
Subject: Hello
X-PHP-Originating-Script: 516:class.phpmailer.php
Date: Fri, 16 May 2014 13:50:52 -0400
From: <redacted>
Reply-To: <redacted>
Message-ID: <redacted>
X-Priority: 3
X-Mailer: PHPMailer 5.2.7 (https://github.com/PHPMailer/PHPMailer/)
MIME-Version: 1.0
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: 8bit
Hello again! Check out the headers.<br><br><br><span><br><br><br><br>
Sent from <a href="https://protonmail.ch" rel="nofollow" target="_blank">ProtonMail</a>,
encrypted email based in Switzerland.</span>
Compared to an encrypted email sent to the same recipient...
Code:
Return-path: <redacted>
Envelope-to: <redacted>
Delivery-date: Fri, 16 May 2014 11:00:09 -0700
Received: from mail.protonmail.ch ([37.35.106.36]:40035)
by whub39.webhostinghub.com with esmtps (TLSv1:DHE-RSA-AES256-SHA:256)
(Exim 4.82)
(envelope-from <redacted>)
id 1WlMQT-00008e-AN
for <redacted>; Fri, 16 May 2014 11:00:09 -0700
Received: by mail.protonmail.ch (Postfix, from userid <redacted>)
id 44B6E14250685; Fri, 16 May 2014 18:00:00 +0000 (UTC)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=protonmail.ch;
s=default; t=1400263200;
bh=aGp26359f4l3hZZUOsTPZ3Swr51EiulknibPVn6xR+I=;
h=To:Subject:Date:From:Reply-To;
b=JSaMJnehESv5RB8bFM+YiYxUIHCdVOachlFAvT8bOeejplvrt16wG6nQG73D/AnB4
jPRMfzy513TjLelKROWE16a8sP9Z86KvIeIAK1WttMuxh+cmznRZRQtJSIipqNat7W
uRz79yBhERKA6N+1B9eicYNXDbxTuOP7x1EqQ/wE=
To: <redacted>
Subject: Hello Again
X-PHP-Originating-Script: 516:class.phpmailer.php
Date: Fri, 16 May 2014 14:00:00 -0400
From: <redacted>
Reply-To: <redacted>
Message-ID: <redacted>
X-Priority: 3
X-Mailer: PHPMailer 5.2.7 (https://github.com/PHPMailer/PHPMailer/)
MIME-Version: 1.0
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: 8bit
Hello,<br><br>You received an encrypted email from the ProtonMail user rockman.
The link to view the encrypted message is:<br>
https://protonmail.ch/decrypt_outside.php?Sender=rockman&Tag=14002632008aeca3fb6a959bd59030<br><br>
The messsage will expire at:<br>2014-05-30 18:00:00 GMT<br><br>
The hint of the password is:<br><br><br>Best wishes,<br>ProtonMail