Re: master 42596bd 2/6: Little improvements in rmail.el. Recognize encryped override headers.

[Gregory Heytings]

> > > +    ;; Debbugs sometimes adds `[External] :'; if that happened,
> > > +    ;; delete everything up thru there.  Empirically, that deletion makes
> > > +    ;; the Subject match the other messages in the thread.
> >
> > This is not accurate -- it's just Drew that insists on adding that 
> > string to his subjects.  I find it pretty odd to add general code to 
> > Emacs to handle a single person's Subject mangling.
>
> I don't think Drew does this himself.  It's probably something that the 
> MTA (mail transport argent) from Oracle adds.  I've seen similar 
> behavior from other people on other mailing lists, most often with 
> [External] or [EXTERNAL], so I would make the comparison 
> case-insensitive.

See https://its.uiowa.edu/support/article/114496 for a possible 
explanation.  This is typically something big corporations or government 
agencies do; for another example on this mailing list, see the posts from 
Stephan Mueller (microsoft.com), which use [EXTERNAL].