Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!aplcen!jhunix!ecf_hap
From: ecf_hap@jhunix.HCF.JHU.EDU (Andrew Poling)
Newsgroups: comp.mail.sendmail
Subject: Re: How to recognize domain literals (was Re: How to use IP addresses ...)
Keywords: canonicalization, MX lookups
Message-ID: <3504@jhunix.HCF.JHU.EDU>
Date: 4 Dec 89 18:41:53 GMT
References: <8911292029.AA13662@jvncf.csc.org> <wZRL3aK00VsLA11Y1Z@andrew.cmu.edu> <1436@utkcs2.cs.utk.edu> <3472@jhunix.HCF.JHU.EDU> <1439@utkcs2.cs.utk.edu>
Reply-To: andy@gollum.hcf.jhu.edu (Andy Poling)
Followup-To: comp.mail.sendmail
Organization: The Johns Hopkins University - HCF
Lines: 47

In article <1439@utkcs2.cs.utk.edu> moore@cs.utk.edu (Keith Moore) writes:
>In article <3472@jhunix.HCF.JHU.EDU> ecf_hap@jhunix.UUCP (Andrew Poling) writes:
>>Wail hail, it's even easier than that if you have functional $[ and $]
>>canonicalization.  In that case, attempting to canonicalize the address
>>should return the hosts domain name anyway.
>
>This can cause delivery failure for outgoing mail to domain literals,
>given the following set of conditions:
>
>1)  $[ IP-address $]  yields  "domain.address"
>2a) DNS lookup of "domain.address" for record type MX yields a host with
>    a different IP address, or

	This is not a concern when using $[ and $] - they simply return the
	full domain-name for the hostname or address contained within them.
	The MX lookup is done later when attempting to connect for delivery.

>2b) DNS lookup of "domain.address" for ADDR record yields a different IP
>    address than in the original domain literal.
>
>I've actually been bitten by the situation described in 2b.  Furthermore,
>even though I could identify the problem using nslookup, I had no way
>of sending mail to the postmaster or system maintainer at that site.

	This is out of your hands if it happens - they're screwed and
	they'll have to fix it.  You can always talk to their SMTP daemon
	and get them mail the hard way though.  I keep a specially
	configured old dumb sendmail around for just this purpose - I type
	too poorly to interact with the SMTP daemon directly.

>Well, support for $[ and $] (at least via the /etc/hosts file) has been
>in sendmail since version 4.39, dated August 1984.  Any one on the Internet
>that is using something older should certainly ftp the latest sources
>from Berkeley and compile them :-).

	Spoken like a man with a VAX and BSD.  Alot of people are trying to
	get what their vendor gave them to work.  I can name examples of
	vendor-released sendmail binaries where the host table based $[ and
	$] simply don't work.

-Andy

--
Andy Poling                              Internet: andy@gollum.hcf.jhu.edu
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