out of place mx records.

[Mark Andrews]

In message <458977.96237.qm at web53606.mail.re2.yahoo.com>, Fr34k writes:
> > In message <barmar-ED15C5.21262028102010 at news.eternal-september.org>,  Barr
> y 
> >Mar
> > golin writes:
> > > In article <mailman.585.1288263412.555.bind-users at lists.isc.org>,
> > >   Tony Finch <dot at dotat.at> wrote:
> > > 
> > > > On  Thu, 28 Oct 2010, Gregory Machin wrote:
> > > > >
> > > > > My  question is why would "IN    MX    10     mcvpemr01" and "IN    M
> X
> > > > >  10     mcvpemr02" be repeated trough the zone file surely this is
> > > > >  redundant ?
> > > > 
> > > > Some hostmasters like to ensure that mail  is not directed to hosts tha
> t 
> do
> > > > not listen on SMTP. They prefer  misdirected mail to be rejected
> > > > immediately rather than waiting  days for the sending system to time ou
> t.
> > > > Some of my colleagues have  this setup on the zones they manage
> > > > (eng.cam.ac.uk and  cl.cam.ac.uk).
> > > 
> > > But configuring MX records won't necessarily  accomplish this.  It will 
> > > cause mail for all these hosts to be  delivered to mcvpemr01 or mcvpemr02
> .
> > 
> > And they can do a SMTP level  rejection rather than waiting for the
> > sending server to abandon sending the  email due to multiple timeouts.
> > Just return 550 for all mail directed to  users at those hosts.   It
> > would be nice if we could standardise a MX  target of "." as saying
> > that this domain doesn't accept email e.g. "MX 0 ."  the same way
> > as "SRV 0 0 0 ." means that there is no service for the  named
> > protocol.  That way the sending MTA or the MSA can reject the  email.
> > 
> 
> Hello,
> 
> Is there an advantage to process email just to have the destination MX reject
> it?
> 
> Why not use " IN MX 100 localhost" so the email doesn't even leave the source
> ?
> 
> Or, am I confused?

Think about the error messages that will be sent.  You want these to
be meaningful.

"550 User unknown.  Please use user at example.com instead."
"550 User unknown.  host.example.net is not a valid email destination."

Messages about mailing looping, which is what you get when you say
localhost, are not very informative.

Mark
-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org