On Saturday, 26 May 2018 at 22:18, Van L wrote:
>> What is your `org-file-apps’?
>
> Value:
> ((auto-mode . emacs)
>  ("\\.mm\\'" . default)
>  ("\\.x?html?\\'" . default)
>  ("\\.pdf\\'" . default)
>  (t . emacs))
> Original value was 
> ((auto-mode . emacs)
>  ("\\.mm\\'" . default)
>  ("\\.x?html?\\'" . default)
>  ("\\.pdf\\'" . default))
>
> It is working now since I was advised to look there and I made the
> above change.

Thanks for this.  I had been struggling to figure out why opening an
attachment directory did not use Emacs (it used to just fine but
something changed over the past months).  Adding that last line makes it
work.  

I think having '((t . emacs)) alone will suffice for me.  I mean, why
would I want to invoke something other than Emacs? ;-)

-- 
Eric S Fraga via Emacs 27.0.50, Org release_9.1.6-591-gee336b