Configuring what program to use to open what file is quite straight forward:
Only problem is, when I did that, I got:
Warning: package evince listed in /etc/mailcap.order does not have mailcap entries.
The man-page for
mailcap.order helpfully says: "Remember that this files [sic] takes package names and not executable names."
But, the command "
evince" comes in the package called "evince", so I assumed the "package name" was "evince". That holds for "
eog", which comes in the package "eog", and is also a GNOME application, as far as I know, and which
update-mime doesn't complain about.
strace -e openat to the rescue, and - hey presto - it turns out the "package name" for evince is "org.gnome.Evince". I plopped that into
mailcap.order, and now Bob's my uncle. Nice to know.