Probably terribly amateurish:
I want to add a header to mail I receive that is in html format. Some
times the "Content-Type:" message isn't in the head of a message but in
the body. So to make a simple header that indicates an html formated
message I'm using this home-boy procmail recipe:
* ^Content-Type: text/html
| formail -I "X-HTML: HTML message" >> /var/spool/mail/reader
No doubt this will introduce horrible locking problems, but I couldn't
quite figure out how to do this more elegantly, without a redirect but
still have the mail land in $DEFAULT mail box. I do further
processing from that point with "Gnus".
My News/Mail reader (Gnus) has machinery that can recognize this
header and put an "HTML" into the summary buffer formatting. So that
it is apparent immediately that this message is HTML, giving me the
choice then, of marking read (deleting) or opening.
I rarely find a message I want to read in Mailing lists, that is in
html format so this provides a way to trash it with out even opening.
There are probably more and better ways to go about this.