Path: utzoo!utgpu!watserv1!watmath!att!linac!pacific.mps.ohio-state.edu!zaphod.mps.ohio-state.edu!usc!ucla-cs!twinsun!eggert
From: eggert@twinsun.com (Paul Eggert)
Newsgroups: news.software.nntp
Subject: Re: NNTPD hates Message-IDs with TWO '@'s in them.
Message-ID: <1991Jun19.201959.20158@twinsun.com>
Date: 19 Jun 91 20:19:59 GMT
References: <1991Jun16.063341.13609@kithrup.COM> <6021@gazette.bcm.tmc.edu> <1991Jun17.193252.28272@zoo.toronto.edu> <5127@lib.tmc.edu> <kre.677336790@mundamutti.cs.mu.OZ.AU>
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kre@cs.mu.oz.au (Robert Elz) writes:

>I would submit that <...@cs.mu.oz.au> is a perfectly good Message-ID ...

At first I thought the same thing, but when I wrote a Message-ID
checker directly from the spec I discovered that I was wrong.
The relevant part of the RFC 822 grammar is:

	local-part  =  word *("." word)
	word        =  atom / quoted-string
	atom        =  1*<any CHAR except specials, SPACE and CTLs>
	specials    =  ... / "." / ...

That `1' is easy to miss, but it means atoms can't be empty, and
therefore `.'s can't begin or end a local-part, and unquoted `..'
cannot appear anywhere in a local-part.