[dns-operations] A problem with using DNAMEs in reverse lookups

Florian Weimer fweimer at bfk.de
Sun Apr 3 15:12:10 UTC 2011

* Jeroen Massar:

> According to the SMTP RFCs an MX effectively becomes a single host, and
> one should connect to first the AAAA addresses and then the A addresses
> till you get an SMTP session. When that session says 3xx you should try
> the next MX, not that same MX on a different address. When you get a
> 4xx/5xx you should fail.

Which SMTP version are you talking about?  There are significant
differences.  IIRC, both RFC 821 and 2821 require that you try other
mail exchangers after hitting a 5xx permanent error, so I wouldn't
read too much into them as far as retry behavior is concerned.

Florian Weimer                <fweimer at bfk.de>
BFK edv-consulting GmbH       http://www.bfk.de/
Kriegsstraße 100              tel: +49-721-96201-1
D-76133 Karlsruhe             fax: +49-721-96201-99

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