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Re: What does this message mean?

On Fri, Dec 01, 2000 at 07:36:54PM +0100, Ralf Baechle wrote:
> Since the recent zmailer upgrade I had several bounces like:
>   Original Recipient:
>     rfc822;foo@bar.de
>   Control data:
>     smtp frob.de foo@bar.de 99
>   Diagnostic texts:
>     smtp; 500 (DNS: MX host does not support SMTP: bar.de)
> What is causing a ``MX host does not support SMPT:'' error?
> I was speculating it might be related to WKS records without SMTP but none
> of the MX hosts has a WKS record at all.

	It depends ... I used to get those too, not anymore.
	(And no, it isn't WKS related. See man-page of 'smtp' about WKS.)

	Over past 3-4 weeks I have had these bounces only when
	- somebody is just changeing DNS zone datasets, and/or
	- MX defined target system does not have A-record
	(They are very rare now. 0-1 per week.)

	The system is somewhat sloppy here, it uses  getaddrinfo(), which
	like  gethostbyname()  resolves text representation of addresses
	and CNAME redirection of DNS lookups.

	The DNS specification says that the MX value must be hostname, and it
	must have an address, specifically CNAME is not valid target for MX.

	If you have a system with its local  getaddrinfo(),  do try to check
	if it *really* works, or does it fail wrong way in case of timeouts
	on the lookups ?  (Linux glibc 2.1 fails ... 2.2 is propably ok,
	not sure of other versions.)

	  cd transports/smtp; make;
	  ./getmxrr-test timeout-mx.zmailer.org

	That should give "temporary failure in name resolution",
	glibc 2.1 gives  ...  Odd, now I can't check that, where
	are my glibc 2.1 machines ... hmm...

	Anyway, it was something else than "temporary" error.

	For that reason the configuration system has option:

>   Ralf

/Matti Aarnio	<mea@nic.funet.fi>