From: Sahil Tandon (sahiltandon.net)
Date: Mon Jul 13 2009 - 19:05:14 CDT

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On Mon, 13 Jul 2009, Benny Pedersen wrote:

> On Sun, July 12, 2009 22:47, Sahil Tandon wrote:
> > On Sun, 12 Jul 2009, Keld Jørn Simonsen wrote:
> >
> >> >> Anyway if it is a name server timeout, then I think this is always
> >> >> handled by a 450 response. In my case the mail was rejected.
> >> >
> >> > Yes, temporary errors always get a 450 response.
> >>
> >> Then I do not understand why the message was rejected. A temporary error
> >> should not result in a reject, or why should this happen?
> >
> > A 450 response *is* a reject;
>
> defer not reject

An irrelevant semantic debate. See postconf(5); it is colloquially common to
refer to these as *reject* codes. What matters is the numerical SMTP
reply code and what it communicates to the client.

> > the 4xx SMTP reply code tells the sending
> > server to queue and try again later.
>
> correct, eg try until sending server have solved reverse dns (unknown)

More generally, a 4yz response simply indicates a transient error, not
necessarily one related to reverse dns. The client should try again.

> > This contrasts with 5xx rejections
> > which are permanent,
>
> one can argue we should not let the sender sever retry on missing reverse
> dns, but it could as well also be errror in recieving side

This (not letting sending server retry in case of DNS problems) would be a
bad argument.

--
Sahil Tandon <sahiltandon.net>

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