Le problème ne provient pas de mon serveur ni de son association à un MX record, le problème provient de leur coté car leur postfix n'associe le MX record qu'à du A record, pas du AAAA record
Hors, d'après la
RFC5321 :
Fallback to the address record
In the absence of an MX record, email senders will attempt delivery to the address record - e.g. example.com.
This is based on RFC 5321 sec. 5.1, which states :
SMTP clients must look up an MX record;
If (and only if) no MX record for the domain is present, treat the domain as if it had an MX record with the given domain as the target hostname and a preference value of 0
Perform A or AAAA lookups as required to determine the IP address of the target hostname
Il serait peut-être temps qu'ils se mettent à jour du point de vue config de leur postfix car il y a pénurie de A record depuis 10 ans déjà et progressivement remplacé par du AAAA record
Car (cfr RFC 5321 sec 5.2) :
5.2. IPv6 and MX Records
In the contemporary Internet, SMTP clients and servers may be hosted
on IPv4 systems, IPv6 systems, or dual-stack systems that are
compatible with either version of the Internet Protocol. The host
domains to which MX records point may, consequently, contain "A RR"s
(IPv4), "AAAA RR"s (IPv6), or any combination of them. While RFC
3974 [39] discusses some operational experience in mixed
environments, it was not comprehensive enough to justify
standardization, and some of its recommendations appear to be
inconsistent with this specification. The appropriate actions to be
taken either will depend on local circumstances, such as performance
of the relevant networks and any conversions that might be necessary,
or will be obvious (e.g., an IPv6-only client need not attempt to
look up A RRs or attempt to reach IPv4-only servers). Designers of
SMTP implementations that might run in IPv6 or dual-stack
environments should study the procedures above, especially the
comments about multihomed hosts, and, preferably, provide mechanisms
to facilitate operational tuning and mail interoperability between
IPv4 and IPv6 systems while considering local circumstances.