Re: [Exim] domain trouble

Just one note - speaking as someone quite familiar with DNS, I am
fairly certain that the DNS system permits only letters, digits and
dash.


On Tue, 5 Sep 2000, Philip Hazel wrote:

> On Mon, 4 Sep 2000, Tabor J. Wells wrote:
>
> > > I can't send messages from the follow domain:
> > > auditores_consultores.com.ec
> > >
> > > That is a registered domain but Exim say:
> > > "unrouteable mail domain auditores_consultores.com.ec". Why?.
>
> > Wow. I'm surprised the .ec TLD administrars would allow that as a
> > registration. Underscores ('_') have never been valid in hostnames or domain
> > names Only letters, numbers, and hyphens ('-') are legal characters. See RFC
> > 952 for details.
>
> I must be pedantic here. As far as the DNS goes, almost any characters
> are valid in domain names. The restriction to letters digits and
> underscores is in RFC 821, the SMTP specification. This restriction
> applies to email domains for messages that are transmitted over SMTP.[*]
>
> Because many host names are also email domains, this effectively
> constrains host names to the same set of characters (and also MX domain
> names of course). It has led to a popular misconception that *all*
> domain names are so restricted, which is not the case. You can have a
> host name containing an underscore, as long as nobody ever uses that
> name as an email domain.
>
> The reason Exim refuses to route to the domain in question is that it
> does a preliminary syntax check before trying to look up the domain
> name. This is done because some DNS resolvers have been found to give
> temporary system errors when presented with syntactically invalid names
> instead of "no such domain". The default syntax check allows only the
> RFC 821 characters. You can change this behaviour by means of the
> dns_check_names and dns_check_names_pattern options. However, I would
> not advise this in this case; it would be far better to get the DNS
> entries fixed to conform to RFC 821.
>
> -----------------------
> [*] Note that RFC 822, which specifies the format of messages, allows a
> much wider set of characters in domain names. You can, in theory, use
> all sorts of characters, provided that the message never goes anywhere
> near SMTP. Needless to say, in practice, these days, this is pretty
> unlikely.
>
>

--