Michael Stone wrote about inserting custom headers automatically in certain
(but not all) outgoing mail,
| I'm not sure this is really a good use for procmail; IMHO, it's more of
| a MUA issue. Take a look at mutt, for example, which allows you to bind
| an arbitrary command (including custom headers) to a regexp based on the
| recipients' addresses.
That facility in Mutt is not only rare among MUAs; it is also, as Michael
described it, much less versatile than what a procmail rcfile for outgo-
ing mail can do.
Many MUAs, including Mutt (unfortunately not Elm), allow setting a filter
for outgoing mail instead of handing it directly to the MUA. procmail's
-m option is perfect for that, and a procmail rcfile can base decisions
on custom headers (or anything) else on more criteria than just the reci-
pients' addresses; it can also consider the subject, the contents, the body
size, the time of day, the day of the week, or what have you as well as
the recipients' addresses.
So I feel that this *is* a good use for procmail.