title: Sending an unsent EML with a specified 'From'-address
body: <p>For an application we want to offer our users generated EMLs which they can open in Outlook 2010 and send after doing minimal changes to the contents of the mail or adding attachments or recipients. One of the things we set when generating the EML is the 'From'-address, which we set to a Mailbox. All users have access to this mailbox but when they open the EML and try to send it, an error is always returned:</p>
  
  <pre><code>Delivery has failed to these recipients or groups:
  
  recipient1@foo.com
  You can't send a message on behalf of this user unless you have permission to do so. Please make sure you're sending on behalf of the correct sender, or request the necessary permission. If the problem continues, please contact your helpdesk.
  </code></pre>
  
  <p>However if the user opens the mail, sets the mailbox manually by selecting the mailbox in the 'From'-combobox (note that nothing visually changes in the email) and then sends the mail, the mail is successfully delivered. It seems to me that I'm missing something in the EML in order to successfully specify the 'From'-address. I'd like to believe that the mail should be able to be sent successfully as long as the user, opening the mail, has access to the mailbox.</p>
  
  <p>An example of an EML is the following:</p>
  
  <pre><code>From: Test-Mailbox@foo.com
  To: recipient1@foo.com, recipient2@foo.com
  Cc: ccRecipient@foo.com
  Bcc: bccRecipient@foo.com
  Message-ID: &lt;29094346.1.1409121155408.JavaMail.tester@wd34376&gt;
  Subject: subject
  MIME-Version: 1.0
  Content-Type: multipart/related; 
  boundary="----=_Part_0_30562042.1409121155299"
  X-Unsent: 1
  
  ------=_Part_0_30562042.1409121155299
  Content-Type: text/html; charset=UTF-8
  Content-Transfer-Encoding: quoted-printable
  
  body goes here
  ------=_Part_0_30562042.1409121155299--
  </code></pre>