On Fri, 06 Jan 2012 10:51:47 +0000, Mark Walters <markwalters1009@gmail.com> wrote:
> > Presumably something is converting it from 8bit to base64 along the
> > path.
> 
> If it makes a difference my setup is gmail->offlineimap->notmuch

Mine is the same for the relevant messages.

> > I scouted around for other messages that include © (which is what I
> > presume causes the encoding), but the ones I have are all still 8bit.
> 
> A different example which shows the same problem (for me) is
> id:"m2fwg1uapw.fsf@gmail.com"

This one is encoded as quoted-printable. I agree that the output of
     | cat >/tmp/file
in the emacs UI produces the encoded file and that it is identical to
the file on disk.

Hence, I can reproduce the problem you reported :-)

(Maybe amusingly) the printing stuff that you originally mentioned
included some code to produce a 'text' version of a message for
printing. Maybe that could also be used to implement a simple
`notmuch-show-save-message' command?