Hi,

does the postfix smtp client implement the IPv6 to IPv4 fallback
mechanism as browsers do?

Postfix implements the MX fallback strategy as defined in the SMTP
RFC (5321). In addition, Postfix implements this:

smtp_address_preference (default: any)
      The address type ("ipv6", "ipv4" or "any") that the Postfix SMTP client
      will try first, when a destination has IPv6  and  IPv4  addresses  with
      equal  MX preference. This feature has no effect unless the inet_proto-
      cols setting enables both IPv4 and IPv6.  With Postfix 2.8 the  default
      is "ipv6".

      This feature is available in Postfix 2.8 and later.

        Wietse

It works with 1 mx with A and AAAA records.

It didn't work with 2 mx with both A and AAAA records
(https://bugzilla.redhat.com/show_bug.cgi?id=813863).

What is your smtp_address_preference setting?

$ postconf smtp_address_preference
smtp_address_preference = ipv6

RTFM (see above) or upgrade.

Sure I have a problem with the idiom, but I'm trying to understand the paragraph above. Why trying first IPv6 implies IPv4 is not going to be used later? And why it does work with 1 MX and id doesn't work with 2 MX? (with equal MX preference in both cases)

--
Un saludo.
Fernando.

---------------------------------------------------------------
Fernando Gozalo Rodrigo - Analista de Sistemas

    Centro de Sistemas Informáticos
Universidad Nacional de Educación a Distancia

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