PRB: ContentClass and Custom Properties Not Supported at Attachment Body Part

Steps to Reproduce Behavior

1. In Microsoft Visual Basic, create a new Standard EXE project.
2. Add a button to the default form and paste the following code into the button's Click event:

       Dim iMsg As CDO.Message
       Dim iConf As CDO.Configuration
       Dim iBp As CDO.IBodyPart
       Dim Flds As Fields
       Dim Strm As Stream
     
       Set iMsg = CreateObject("CDO.Message")
       Set iConf = iMsg.Configuration
       iConf("http://schemas.microsoft.com/cdo/configuration/sendusing") _
           = cdoSendUsingExchange
       iConf.Fields.Update
       
       'TO DO: Change From and To
       iMsg.To = "someone@somewhere.com"
       iMsg.From = "someone@somewhere.com"
       iMsg.Subject = "subject"
       iMsg.TextBody = "text body"
       Set iBp = iMsg.AddAttachment("")
       iBp.ContentClass = "urn:somewhere:mycc"
       Set Flds = iBp.Fields
       Flds("urn:schemas:mailheader:content-type") = "text/html"
       Flds("urn:schemas:mailheader:content-class") = "urn:somewhere:mycc"
       Flds("urn:schemas:mailheader:mycustomprop") = "myproperty"
       Flds.Update
       Set Strm = iBp.GetDecodedContentStream
       Strm.WriteText "Attachment body part new text", adWriteLine
       Strm.Flush
       iMsg.Fields.Update
       iMsg.Send
       Set iMsg = Nothing
    
   					

3. Change the e-mail address of iMsg.To and iMsg.From in the code.
4. Add a reference to Microsoft CDO For Exchange 2000 Library and Microsoft ActiveX Data Objects 2.5 Library.
5. Run the program and click the button to send the message.
6. Observe the MIME stream of the received message. The attachment body part's ContentClass property and urn:schemas:mailheader:mycustomprop custom property are not persisted.