Thank you for your question below.
As far as I am aware there is no 100% reliable method by which you could determine if the original message is attached (or inlined) in the current message.
You would probably need to iterate through the attachments collection of the current message looking for attachments of type message. For each message attachment found, you would need to make a determination if the message looked like the original. The subject may be the only common information you could use.
If no message attachments were found, you would then search the body text of the current message looking for inline message text, extracting the subject, and making the same evaluation. Again, the reliablity of this technique is unknown.
In both cases you’ll want to work with the CommandMessage object obtained via:
Set Msg = Client.ClientState.CommandMessage
This will give you a true Object API message object, making it easy to access it’s attachments collection, etc.
I hope this helps.