Newsgroups: comp.mail.headers
Path: utzoo!utgpu!jarvis.csri.toronto.edu!neat.ai.toronto.edu!lamy
From: lamy@ai.toronto.edu (Jean-Francois Lamy)
Subject: Re: "X-" blithering
Message-ID: <88Aug3.094652edt.66@neat.ai.toronto.edu>
Organization: Department of Computer Science, University of Toronto
Date: Wed, 3 Aug 88 11:06:25 EDT

Resonable mail user interfaces allow you to filter whatever you consider to
be blithering.  X-whatever headers are defined in RFC-822 to be extensions
to the standard set.  Mailers on Symbolics lisp machines, for example, use
such headers to document what the control sequences in the messages mean,
so that the recipient can see the italics the sender put in.  Other purported
uses would be documenting the encoding format of a message (e.g. uuencoded),
so that a co-operative mail user agent knew how to deal with them.

As to the infamous X-Mailer: ..., consider it to be gratuitous publicity, just
like having your car dealer's sticker on your car.  My mail set-up zonks that
one into oblivion.

The X-VMS-To: header is actually useful if you have to deal with the
brain-dead mailer that DEC gives with VMS: the interpretation of the % sign is
radically different than the usual subsitution for "@", and is a signal that
you are probably asking for trouble if you trust the mailer provided return
address.

All in all, no, there is absolutely no link with X.

Jean-Francois Lamy               lamy@ai.utoronto.ca, uunet!ai.utoronto.ca!lamy
AI Group, Department of Computer Science, University of Toronto, Canada M5S 1A4