On Fri, 2007-06-15 at 17:57 +0200, Renaud Allard wrote:
>
> Leonardo Boselli wrote:
> > Some user had voicely complained me that one of thetir correspondent
> > (say mario@??? -fictitious-) has all his e-mail rejected.
> > I checked and turned that the server, that officially has the name
> > mail.ditchedserver.org, send this helo:
> > HELO ISCRA_domo.arsi
> > (and this name is the real one that send !)
> >
> > my exim 4.63 is unhappy and reject immediately the connection saying there
> > is an illegal (I suppose '_' )characther in helo name.
> >
[chop]
> >
> > In alternative: can some one give me a link to some offical rule saying is
> > not acceptable sending Helo with underscores or non existant FQDN ?
> >
>
> Hello
>
> quoting RFC2821 paragraph 4.1.2:
> In
> particular, the underscore character is not permitted. SMTP servers
> that receive a command in which invalid character codes have been
> employed, and for which there are no other reasons for rejection,
> MUST reject that command with a 501 response.
In addition, underscores are illegal for host names on the internet, as
per <URL:
http://tools.ietf.org/rfc/rfc952.txt>. Underscores are now
used for special purposes within DNS (like SRV records), but should
never appear in a real hostname.
The main problem is that some operating systems allows setting the
hostname to a name with an underscore. Which is well and fine as long
as you don't connect to the Internet. These guys will see a whole bunch
of problems for any service that wants to look up their hostname due to
this. Or rather, the remote users will see the problems.
> If you wish to accept them, you can put in your config:
> helo_allow_chars = _
That won't help if using helo_verify and the DNS is (correctly)
rejecting queries for hostnames containing illegal characters.
Regards,
--
*Art
