Hello,

kindly find below a patch which I have been using in my local setup for
about a year without seeing any hiccups. So I thought it would be worth
proposing to the developers.

The issue I saw with S/MIME encrypted messages was, that the processing
of the MIME tree stopped after decryption. It turned out there was no
handler for application/(x-)?pkcs-mime type entities in notmuch-show.el,
and the "handler of last resort" notmuch-show-insert-part-*/* was
called. Thus, this patch just adds a notmuch-show handler for
application/(x-)?pkcs-mime type entities.

RFC 8551 defines that there is a single child element only ("A body can
consist of a single MIME entity or a tree of MIME entities (rooted with
a multipart).", clause 3.1), hence no list processing of the children is
needed (there's only one).


Hoping to have helped, and looking forward to your thoughts,

  --alexander