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.
--
Philip Hazel University of Cambridge Computing Service,
ph10@??? Cambridge, England. Phone: +44 1223 334714.
