[Mimedefang] Non-routable addresses in HELO

Steffen Kaiser skmimedefang at smail.inf.fh-bonn-rhein-sieg.de
Tue Jul 11 06:37:44 EDT 2006

On Tue, 11 Jul 2006, Jan-Pieter Cornet wrote:

> So, based on this latter paragraph, it is entirely OK to reject
> after "EHLO", 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:


relevant EBNF:

             <domain> ::=  <element> | <element> "." <domain>

             <element> ::= <name> | "#" <number> | "[" <dotnum> "]"

             <dotnum> ::= <snum> "." <snum> "." <snum> "." <snum>

             <number> ::= <d> | <d> <number>

             <snum> ::= one, two, or three digits representing a decimal
                       integer value in the range 0 through 255

EHLO's argument is defined more restrictive.

BTW: That somebody knows what the "#" <number>  element is used for?


Steffen Kaiser

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