188.8.131.52.1.2 Converting a Clear-Signed Message in Internet Format into a Message Object
Create an Attachment object.
Set Attachment object properties, as specified in section 184.108.40.206.
Remove all header fields except the Content-Type header field, as specified in [RFC2045] section 5, from the message MIME entity.
Save the resulting MIME entity as content of the Attachment object created in step 2. For example, set the value of the PidTagAttachDataBinary property ([MS-OXPROPS] section 2.589) on the Attachment object.