One of my colleagues has started signing mail like so:

Content-Type: multipart/signed;
	boundary="Apple-Mail=_753C8B6F-7436-4273-AAD9-DAEE99B4FE59";
	protocol="application/pkcs7-signature"; micalg=sha1

Is there a configuration knob I can turn to have this rendered
correctly (Gnus v5.13 on Emacs 25.1.90)? At present, I just get
the raw text.

                                        Be seeing you,
                                          norm

-- 
Norman Walsh <ndw@nwalsh.com> | What is familiar is what we are used
http://nwalsh.com/            | to; and what we are used to is most
                              | difficult to 'Know'—that is, to see as
                              | a problem; that is, to see as strange,
                              | as distant, as 'outside us'.--Nietzsche