Re: [Exim] Re: Underscore in domain is being rejected

On Sat, 29 Jun 2002, Derrick 'dman' Hudson wrote:

> --
> On Sat, Jun 29, 2002 at 07:25:07PM -0400, Dave C. wrote:
>
> | because neither domain exists (try a whois and/or a dig/nslookup),
>
> | nor _can_ exist.
>
> Never underestimate Windows' potential for stupidity. A windows
> machine can be installed and configured with an underscore in the
> host/domain name. Exchange will then present that name in the EHLO.
> While I don't have direct experience with that, that was the source of
> the complaint regarding the strictness in exim4's helo checking
> option.
>

Oh yes, individual machines can/could be configured to allow that, but
no domain registar will allow the domain to be registered, so any domain
with an underscore is invalid as an email domain so cannot be part of
any legitimate Internet email address, since the domain can't exist for
real on the Internet.

Underscores within hostnames (and presented via HELO) are a different,
but related, problem.


Eg user@foo_bar.com can never be a valid and deliverable email address,
becuase you can never register foo_bar.com with any registrar.
(regardless of the capacity to configure a Wincrap-based server to send
or receive mail using such addresses)

foo_bar.validdomain.com is not valid either, but might be assigned to a
live functioning email server which otherwise correctly handles mail for
valid addresses@???