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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 [email protected] 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 [email protected], which
doesn't exist:

   ----- Transcript of session follows -----
501 5.1.2 [email protected] 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
[email protected]
My opinions DO, in fact, represent the official opinions of North
Shore Technologies Corporation, since I own the company. Thanks for asking.