X-Headers

RFC 2822 says emails can have user defined headers of the form X-header: Usenet posts can have custom headers of this form also.

A popular use of this is the X-Face header.

Here are some other good custom headers I've found in my mailboxes...

http://www.nut.house.cx/~nemo/visible/X-headers

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For myself, I'm planning to steal and create a bunch of X- headers, and mostly use them as an alternative to trying to optimise so much junk in my signature. :) --Nemo

Some of my favourites (ie, ones I plan to use, more or less)

X-Disclaimer: Use of advanced messaging technology does not imply an endorsement of western industrial civilisation.
X-Answer: forty-two
X-AYPWIP: Wuh, I think so Brain, but we'll never get a monkey to use dental floss.
X-Rays: Do not expose this message to X-rays.
X-treme-sport-you-havent-tried-yet: Kissing My Arse
X-Dictionary: Use it to look up more words starting with X.
X-Been-There: Done That. Got the T-shirt.
X-Big-Brother: Is watching you.
X-Battle-Cry: Spoon!
X-Spoon: There is no spoon.
X-Bumpersticker: I brake for rfc2822
X-Go-Away: Or I shall taunt you a second time!
X-Message-Flag: Do not read while operating heavy machinery
X-Spook: Hello to all my Fans in domestic surveillance
X-Subliminal-Message: The Corps is Mother, The Corps is Father.
X-Jedi-Mindtrick: This isn't the email you are looking for
X-Tyler-Durden-says: Make soap.
X-Thanks: TISM, Animaniacs, The Tick, The Matrix, Babylon5, Star Wars, Douglas Adams, Monty Python, Fight Club, George Orwell.
X-Signature: Mostly substituted with X- headers