Fetchmail/Sendmail rejects

[Malcolm Kay]

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.

Malcolm