Re: regarding illegally formed address and commands

Ned Freed <Ned.Freed@innosoft.com> Mon, 23 December 1996 22:42 UTC

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From: Ned Freed <Ned.Freed@innosoft.com>
To: Jack De Winter <jack@wildbear.on.ca>
Cc: ietf-smtp@list.cren.net
Subject: Re: regarding illegally formed address and commands
In-Reply-To: "Your message dated Mon, 23 Dec 1996 14:50:20 -0500" <3.0.32.19961223145019.00eda6dc@lacroix>
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> just out of curiousity, what do people do with
> illegally formed commands?

Depends both on the command as well as what's illegal about it. As another data
point, PMDF will reject a command when the command syntax itself, as opposed to
the arguments to the command, is illegal. When an argument is illegal it
depends on what the argument is used for. In the case of a malformed address
argument to a MAIL FROM command, for example, PMDF doesn't care since it isn't
essential in getting a message delivered, and experience has shown that
rejecting such messages on the basis of a potential problem returning a
nondelivery notification later is not what users want.

PP, on the other hand, is much more picky about this sort of thing. I don't
believe it will let an invalid argument to MAIL FROM through at all.

> I checked around with
> a couple of implementations over the weekend, and
> not one of them did anything seeming intelligent
> if I entered the following lines:

> MAIL FROM:<jack@jacks world%>
>  or
> RCPT TO:<jack@jacks world%>

> No error returns or anything.  Both the '%' and the ' '
> are illegal on the domain name side.

Not quite. The space is certainly illegal, and sure enough when I try these on
PMDF it accepts this MAIL FROM for reasons I have already explained but rejects
this RCPT TO.

However, the % is somewhat more problematic. As far as I know it is
syntactically legal to have it in the domain part of an address. The fact that
there are no valid Internet domains that have a % character in them is a
administrative issue, pure and simple -- as the DNS folks often point out, the
restriction of domain names to alphanumerics plus dashes is purely an
administrative, not a technical, matter, since the DNS can in practice
contain almost anything.

The bottom line is that there is nothing that says a site cannot have an
internal domain specification with a % in it. Private semantic extensions are
nowhere banned by the standards, and even if tried to ban such things we would
simply be making fools of ourselves as modulo syntactic concerns what people do
on their own networks administratively is their own affair. (Just don't let the
gunge leak out onto the real Internet, of course.)

So while a default PMDF configuration for Internet use won't allow this use of
% in a RCPT TO, you can configure things so that it will work. There are, of
course, substantive issues with using %s in particular in domain names because
of the widespread use of poor man's % routing. But PMR is merely a convention;
it is nowhere described in a standard at the present time so you cannot use it
to claim standards incompliance.

				Ned