malcolm.kay at internode.on.net
Sat Aug 14 19:07:40 PDT 2004
On Sunday 15 August 2004 11:26, Malcolm Kay wrote:
> On Sunday 15 August 2004 10:40, Chuck Swiger wrote:
> > Malcolm Kay wrote:
> > [ ... ]
> > > Thanks guys for the responses -- this really looks the way to go.
> > >
> > > Does anyone know how sendmail distinguishes between:
> > > reject=451 4.1.8 Domain of sender address ................ does not
> > > resolve reject=553 5.1.8 .......... Domain of sender address
> > > .............. does not exist It seems the former is to be interpreted
> > > as a 'temporary' condition while the latter is to be interpreted as
> > > 'permanent' (and is by default deleted by fetchmail)?
> > Sendmail pays attention to the return value from doing DNS queries. If
> > sendmail receives an NXDOMAIN response, it treats that as a permanent,
> > 5xx failure code. If sendmail gets a timeout/TRY_AGAIN, it will return a
> > 4xx temp failure.
> This sort of takes us back one more level -- how does the DNS service
> decide between responding with NXDOMAIN and a timeout/TRY_AGAIN? And does
> the difference have any real significance?
> > It's not clear to me why this would matter if your ISP is the one running
> > the mailserver: they aren't accepting the message in either case, which
> > ought to mean that fetchmail will never see it.
> None of it is particularly clear to me -- but apparently my ISP's server is
> not rejecting these messages.
> If all mail servers rejected these messages it would seem to me to make the
> spammers endeavours rather pointless.
Perhaps I've not made it clear that the above reject messages appear in the
maillog on my local machine as a consequnce of fetchmail reposting the messages
to local sendmail.
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