Underscores in host names
Jay R. Ashworth
jra at baylink.com
Wed May 18 02:46:59 UTC 2005
On Wed, May 18, 2005 at 11:08:03AM +1000, Mark Andrews wrote:
> In article <1116377042.592906.137650 at 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 at 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
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