I think the purpose of this protocol is to bundle other data into the smtp requeat. Why not just make a standardised format that can be included as an attachme

I think the purpose of this protocol is to bundle other data into the smtp requeat. Why not just make a standardised format that can be included as an attachment? Or even add special tags within the text of the email? This would achieve the same where you have client support, and not need to spend time writing a protocol.