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From: rickert@mp.cs.niu.edu (Neil Rickert)
Newsgroups: comp.mail.sendmail
Subject: Re: what should maphostname() do when disconnected from the net?
Message-ID: <1991Jun18.232256.23757@mp.cs.niu.edu>
Date: 18 Jun 91 23:22:56 GMT
References: <1991Jun18.200709.18664@watmath.waterloo.edu>
Organization: Northern Illinois University
Lines: 25

In article <1991Jun18.200709.18664@watmath.waterloo.edu> gamiddle@watmath.waterloo.edu (Guy Middleton) writes:
>[Using 5.65+IDA+DECWRL sendmail]
>
>If the nameserver is temporarily out-to-lunch (usually because our link to the
>rest of the net is down), maphostname() (in daemon.c) will fail.  This may
>
>If we're calling $[...$] from the config file to look up a name, it thinks
>that there is no such host.  We have been using the IDA extension to $[...$]

  This is exactly why the IDA/UIUC/NIU rulesets have something like
"if all else fails, try the TCP mailer - there might be an MX record".
(The documentation is arguable bad, but the idea behind it is solid).

 If you send such a message to the TCP mailer, and there is a nameserver
lookup failure, the message will be requeued for later trial.  If the
TCP mailer says 'Unknown host', it says this because the nameserver lookup
was "successful" in returning NXDOMAIN, thus documenting that the name is
not known to the nameservers.  The soft failure you are seeing gives a
nameserver return indicating server failure, and this triggers the requeuing.

-- 
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  Neil W. Rickert, Computer Science               <rickert@cs.niu.edu>
  Northern Illinois Univ.
  DeKalb, IL 60115                                   +1-815-753-6940