We have checked the attached MSG file and saved the attachment to disc which is saved as Journal item to the disc by the API. Following code sample was used to read and save the attachment to disc. Please let us know if you are facing some issue with this along with your sample code you are trying at your end.
MapiMessage mapi = MapiMessage.FromFile("164427\\MSG with Journal Attachment.msg");
MapiAttachment att = mapi.Attachments;
MemoryStream ms = new MemoryStream();
ms.Position = 0;
MapiMessage attMsg = MapiMessage.FromStream(ms);