On 2026-05-25 7:16, Wietse Venema via Postfix-users wrote:
I don't know that a large majority of mail servers has IPv6
connectivity, but the way Postfix implements this feature selection
can be improved.
Definitely not a majority, no. From my own MX log data, I observe
20-25% of "legitimate" mailhosts connecting over IPv6. "Legitimate"
here meaning those hosts that get past postscreen's bot countermeasures
and DNSBLs.
The "make upgrade" mechanism pre-dates "compatibility_level" which
provides a more explicit way to manage changes in default settings
(it would log that it is falling back to IPv4-only).
This does sound like a better way to do it. The main.cf that lacked an
explicit inet_protocols did have "compatibility_level = 3.11", so
postfix would have known I expected the current default.
I ask because I just caught that behaviour during an upgrade test and,
had I not caught it, it would have knocked my publicly-IPv6-only
mailhosts offline.
You upgraded from a configuration that had no explicit inet_protocols
setting?
Yes. It didn't have "inet_protocols = all" because postconf -d said
that was the default when I last reviewed main.cf for redundant
settings. I overlooked the unique handling for inet_protocols.
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