raf/Open attachments in Mutt with your desktop apps

Yes I'm a proud Mutt user, say what you will about user interfaces but no mail client in the known universe can compare to the awesomeness of Mutt.

As ridiculous as this may seem Mutt is not very smart when it comes to attachments, it basically uses the mailcap(4) file to figure what application to open the file with. A mailcap file is basically a mapping between mimetypes and application, for e.g. the following mailcap

text/plain; cat %s
text/html; lynx -display_charset=utf-8 -dump %s

would open text files with cat, and html files with lynx.

The problem with this approach is that you would have to add one line per mimetype, for every single attachment type you want to open. This makes sense for your console environment but looks absurd if you are running a full desktop environment that already knows which applications to use.


Large desktop environments usually have a command to open files with the correct application, i.e. they look at the file extension and mimetype and choose the application you configured for that file type. In GNOME this is called gnome-open and in KDE kde-open. But if you have xdg-utils installed you can simply invoke xdg-open and will use the appropriate program for your desktop environment. So running

$ xdg-open ~/Downloads/1107.5728v2.pdf

should open your PDF viewer.


The problem with using xdg-open with Mutt is that mutt expects the application being called to block until it is finished, but xdg-open will exit as soon as it calls the app. Internally Mutt operates as follows:

  1. Get mailcap mapping
  2. Copy attachment to /tmp folder
  3. Open file with application from mailcap
  4. Wait for application to close
  5. Remove temporary file

The main problem being that Mutt will remove the file after the call is complete which means any application that is called to open the file will be unable to open the file, because it was already removed.

mutt-open is just a shell wrapper around xdg-open, that makes a copy of the file before calling xdg-open. I first saw a script like this in a redhat bug report (see the link at the bottom), I just rewrote it in python and added a couple of changes.

if __name__ == '__main__':

    if len(sys.argv) < 2:
        print('Usage: %s <filename> [suffix]')

    oldfile = sys.argv[1]

    suffix = file_sha1(oldfile) + os.path.basename(oldfile)
    if len(sys.argv) == 3:
        suffix += sys.argv[2]

    #newfile = mkstemp(suffix=suffix, prefix='mutt_bak_')[1]
    newfile = os.path.join('/tmp', 'mutt_bak_' + suffix)

    copyfile(oldfile, newfile)
    call(['xdg-open', newfile])

Do notice that the newly created file is never removed from /tmp, this is mostly fine for me since my system will periodically clean up the /tmp folder.

Finally to make Mutt use mutt-open to open mail attachments you need to add the following to your ~/.mailcap file.

application/*; mutt-open '%s'; test=test -n "$DISPLAY"

This mailcap will use mutt-open for all attachments with mimetype application/*, but you can change the mimetype to be more restrictive. The test= expression at the end of the line is there to ensure that this entry is not used when X11 is not running.

I've also added an optional second argument to mutt-open, to specify a suffix for the temporary file name suffix. This allows me to handle edge cases where the attachment filename has no extension - as is the case with html formatted mails.

text/html; mutt-open '%s' .html ; test=test -n "$DISPLAY"

Remaining issues

There are still a couple of issues left:

  1. The files are never removed from tmp, which may be a problem, depending on how you run your system
  2. For the specific case of opening HTML files, the file encoding might not be your system encoding usually this is fixed by either converting the file on opening, or by specifying the encoding as an argument for the browser