Email attachment contenttype property

如何判断在orchestration中基于POP3协议attachment的类型为email?

v_attachContentType = System.Convert.ToString(MsgPart.GetPartProperty(typeof(Microsoft.XLANGs.BaseTypes.ContentType)));

v_attachContentType = v_attachContentType.ToUpper();

v_isEmailAttachment = v_attachContentType.Equals("MESSAGE/RFC822");