Re: Underscores in host names

["Jay R. Ashworth" <jra () baylink com>]

On Wed, May 18, 2005 at 11:08:03AM +1000, Mark Andrews wrote:
> In article <1116377042.592906.137650 () g44g2000cwa googlegroups com> you write:
> > Hello all.
> > We have a client containing an underscore in the email address domain
> > name.  Our email server rejects it because of it's violation of the RFC
> > standard.  This individuals claim is that he doesn't have problems
> > anywhere else and if this is going to be a problem he's "going to take
> > his business elsewhere"!
> >
> > I understand it's a violation of the standard, but does it pose a
> > security hole to the email server to allow this sort of mail?
>
>       RFC 952 and RFC 1123 describe what is currently legal
>       in hostnames.
>
>       Underscore is NOT a legal character in a hostname.
>
>       Before anyone says that domain names allow underscore which
>       they do.
>
>       RFC 1034 Section 3.3
>
> For hosts, the mapping depends on the existing syntax for host names
> which is a subset of the usual text representation for domain names,  
> together with RR formats for describing host addresses, etc.  Because we
> need a reliable inverse mapping from address to host name, a special
> mapping for addresses into the IN-ADDR.ARPA domain is also defined.
>
>       Mail domains follow the same rules as for hostnames.  RFC
>       821 and its replacement RFC 2821 havn't extended the syntax
>       to include underscores.

Those with long memories will remember when Apple got strict on this
years ago, and lots of websites became unreachable to their users...

Cheers,
-- jra
-- 
Jay R. Ashworth                                                jra () baylink com
Designer                          Baylink                             RFC 2100
Ashworth & Associates        The Things I Think                        '87 e24
St Petersburg FL USA      http://baylink.pitas.com             +1 727 647 1274

      If you can read this... thank a system administrator.  Or two.  --me