[Mimedefang] Non-routable addresses in HELO

[Jan-Pieter Cornet]

On Tue, Jul 11, 2006 at 12:37:44PM +0200, Steffen Kaiser wrote:
> On Tue, 11 Jul 2006, Jan-Pieter Cornet wrote:
> 
> >So, based on this latter paragraph, it is entirely OK to reject
> >after "EHLO 127.0.0.1", since that is not a properly formatted EHLO
> >argument. RFC821 has similar restrictions on the HELO argument,
> >which should be a "domain" (no IP allowed).
> 
> RFC821 is funny, because it allows this:
> 
> [1.2.3.4].[1.2.3.6].#123445.DummDiDumm
> 
[...BNF explantion...]

But there are additional limitations in the text of RFC821, to
quote:

from section 3.5 Opening and Closing:

      HELO <SP> <domain> <CRLF>

from section 3.7 Domains:

      Whenever domain names are used in SMTP only the official names are
      used, the use of nicknames or aliases is not allowed.

And from the glossary:

   domain

      The hierarchially structured global character string address of a
      host computer in the mail system.

And it is indeed fun to read, because the DNS system has only just
been invented when this was written, and that clearly shows :)
 
> BTW: That somebody knows what the "#" <number>  element is used for?

That knowledge might have been lost together with Jon Postel. I've
never seen it used.

-- 
Jan-Pieter Cornet <johnpc at xs4all.nl>
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