Код:

private void MHTFileSaveCreateOverWrite(string sPathToFile, string sFileName, string sURI)
           {
               CDO.Message iMessage = new CDO.Message();
               iMessage.CreateMHTMLBody(sURI, CDO.CdoMHTMLFlags.cdoSuppressNone, "", "");
               ADODB.Stream adodbstream = new ADODB.Stream();
               adodbstream.Type = ADODB.StreamTypeEnum.adTypeText;
               adodbstream.Charset = "windows-1251";
               adodbstream = iMessage.GetStream();
               adodbstream.SaveToFile((sPathToFile + sFileName), ADODB.SaveOptionsEnum.adSaveCreateOverWrite);
               adodbstream.Close();
           }