[pfx] Re: Should the configuration upgrade process still append "inet_protocols = ipv4"?

Mel P via Postfix-users:
>  From the 2.9 release notes:
> 
> - The default inet_protocols value is now "all" instead of "ipv4",
>    meaning use both IPv4 and IPv6.
> 
>    To avoid an unexpected loss of performance for sites without
>    global IPv6 connectivity, the commands "make upgrade" and "postfix
>    upgrade-configuration" now append "inet_protocols = ipv4" to
>    main.cf when no explicit inet_protocols setting is already present.
>    This workaround will be removed in a future release.
> 
> 
> That was from almost 15 years ago.  Is it time to revisit this and allow 
> main.cf without an explicit inet_protocols define?

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.

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).

> 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?

> p.s., If you want an effective anti-spam measure, make your MX 
> IPv6-only.  Most bots are still IPv4-only.  As a bonus, hyperspammers 
> like Microsoft, Sendgrid, and Google massively fail at fallback.  If you 
> don't need broad reach to the general internet, why not?  /sarcasm

I guess that bots are still IPV4-only because that is where most
of the mail servers are. That would be an argument against
unconditionally turning on Postfix IPv6 support.

	Wietse
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