Quoting Paul Johnson, from the post of Fri, 17 Sep:
Very few clients show all the headers.
It doesn't matter, because you can still sort by those other headers.
not really. most of the world (sigh) uses Micro$oft LookOut(tm). I am a happy user of Mutt on Linux, and my mail filteration is a bunch of .qmail files. Never found the need (in 14 years of using Unix) to learn procmail, I have a simple sed script to make my subject pretty. I have many complaints about mailing list servers and users, but this is not one of my problems :-)))