How to clearly recognize an S/MIME message

Having read the two answers (thanks) to my question I get the following
impression:

   Section 3.2.1 should have a sentence added that says something like "Only if
the MIME type of a message is application/octet-stream the receiving agent
SHOULD use the file extension to determine if the message is an S/MIME message.

   I think, this would remedy the apparent contradiction.


   Regards,

   Frank Schwab