Re: Underscores in host names

["william(at)elan.net" <william () elan net>]

On Thu, 19 May 2005, Mark Andrews wrote:

> In article <Pine.LNX.4.60.0505180849230.24969 () hermes-1 csi cam ac uk> you write:
> > There are also mail domains to consider. They have superficially the same
> > syntax as host names (they cannot have a trailing dot) but they are
> > generally checked much more strictly for conformance to that syntax. I'm
> > not sure whether the original post was about a mail domain or the name of
> > a mail host, but if it was the former I would be surprised if the customer
> > could claim that it works most of the time.
>
>         Hostnames can't have a dot at the end either.  The dot at the
>         end is a local resolver indication to not use the search list.

Actually its been discussed and we may yet see trailing in mail address.

The reason why its been considered is that SMTP RFC2821 spec is flowed
as it requires at least one "." in the hostname (unlike DNS specs that
do not have this requirement for hostname) and that means that you can
not accept as valid email address something like "postmaster@tv", i.e.
if TLD is also a valid host you can not have an email address there.

Since changing SMTP2821 and waiting until everyone complies and accepts
email addresses with no "." is not an option, the solutions proposed are 
to either have address like "postmaster@.tv" or "postmaster@tv."

The only reason it has not been discussed more actively is that no TLD 
operator has yet come forward and said that they are going to use 
TLD host for emails, but as soon as one does this would have to be
accommodated and quickly (otherwise it will remain as an open issue for 
future update to SMTP - probably RFC4821 if this numbering continues :)

--
William Leibzon
Elan Networks
william () elan net