Composing a New Message Object that Represents an Opaque-Signed or Encrypted S/MIME Message

To compose a new Message object that represents an S/MIME message, first compose an opaque-signed message or an encrypted message by using the Internet e-mail message format specified in [RFC5751], and then convert that message to a Message object, as specified in section The client SHOULD generate media types using an "x-" prefix; for example, application/x-pkcs7-mime. For more information about the "x-" prefix, see [RFC2311] section C.1. A client can use a different process as long as it results in the same Message object structure and content.