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Re: mail does bounce (was: Customers down?)

  • From: Steven J. Sobol
  • Date: Sat Jan 01 21:42:52 2000

On Sat, 1 Jan 2000 wrote:

> > > I know for certain that Postfix and Smail will immediately bounce a
> > > message when the domain is authoritatively non-existant.  I'd be very
> > > surprised and dismayed if sendmail and all other true SMTP mailers did
> > > not do exactly the same thing.
> > 
> > Sendmail most definitely does not, instead treating the error as a 
> > transient error, issuing an SMTP error code in the 400 series, and
> > continuing to try to send the mail for up to five days (the default),
> > or whatever the mail server admin configured for that particular
> > server.
> > 
> > I think I like it better that way. Just because both nameservers are
> > temporarily down doesn't mean the domain doesn't exist. :P
> Seems to me you're talking past one another. If all nameservers for a
> domain are down there *is* no nameserver which can say that the domain
> is authoritatively non-existent. (OK, you could get a negative caching
> answer from one of the authoritative servers on the level above, but
> that's a different issue...)
> I agree with Greg Woods - if a domain is authoritatively non-existent,
> I'd expect a sane mailer to bounce the message.

Hm. I think you're looking at this from a different angle. Yes. If
the domain can't be found because there are no records in the root
nameserver, a sane mailer should bounce the message, and in fact,
Sendmail does, as shown by the following bounce message from my Sendmail
server after a message to, which
doesn't exist:

   ----- Transcript of session follows -----
501 5.1.2 Host unknown (Name server: host not found)

The 500-series errors are permanent (fatal) failures.

What I was referring to was a situation where the domain does exist in the
root nameservers but the authoritative nameservers are unavailable.

North Shore Technologies  888.480.4NET
Steve Sobol, President, Chief Website Architect and Janitor
My opinions DO, in fact, represent the official opinions of North
Shore Technologies Corporation, since I own the company. Thanks for asking.

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