title: Is it possible to create a signed email with an opaque signature using MimeKit?
body: <p>Basically as the questions states.  </p>
  
  <p>I have written a program to sign an email using an X509Certificate2 installed on a users machine.  This is done with MimeKit, which makes it very easy (as shown).</p>
  
  <pre><code>var signer = new CmsSigner(certificate, key);
  signer.DigestAlgorithm = DigestAlgorithm.Sha1;
  
  message.Body = MultipartSigned.Create(ctx, signer, messageContent);
  </code></pre>
  
  <p>I've just been asked if it is possible to create this signed email using an 'opaque' signature instead of a detached signature.  I believe there is an option in OpenSSL that can do this(??).  </p>
  
  <p>Anyway, I've been unable to find any mention of an 'opaque' option in relation to MimeKit.  </p>
  
  <p>Is this possible, and if so, how?</p>