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

$ postconf inet_protocols
inet_protocols = all

--
Un saludo.
Fernando.

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

    Centro de Sistemas Informáticos
Universidad Nacional de Educación a Distancia

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