Origin of the percent sign

[Usenet file owner]

I have a question for all you network trivia people.  Where lies the
origin of the percent sign in mail (ie weaver%mach1 at gate1)?  I have
read rfc822, rfc733, and even rfc561 with no luck.  Is this an
aberration of the above, or just some widely accepted nonstandard?

Mail to me and I will post the answer to save bandwidth...

Thanks in advance

Jeff Weaver
Ford Motor
weaver at pms018.pms.ford.com