How to prevent, or change priority, of dovecot's FAILed relay-submission to relay's IPv6 address, and submit ONLY/first to IPv4?

[PGNet Dev]

On 4/9/21 8:08 AM, @lbutlr wrote:
> On 08 Apr 2021, at 06:08, PGNet Dev <pgnet.dev at gmail.com> wrote:
>> whereas other services listen at both IPv4 & IPv6 addresses, with IPv6 preferred over IPv4, postfix listens ONLY on IPv4,
> 
> Do you mean that YOUR postfix only listens to ipv4?

Yep.

> If so, wouldn't the solution be to setup postfix to listen to ipv6?

That would work, of course, but that's not the point.  I'm not planning to open postfix listener on the public IPv6 in order to accommodate one service connection (Dovecot's relay submit), only to have to add add'l knobs to lock down access.

And it's a bad assumption that since the host is dual-stack that all services on it will be.

The 'solution' is to have Dovecot relay submit connect where & how you TELL it to connect, NOT where it assumes it's OK to connect.

It's already possible to set

  submission_relay_host       =
  submission_relay_port       =
  submission_relay_ssl        =
  submission_relay_ssl_verify =
  submission_relay_trusted    =

in order to specify exactly how/where to securely connect for relay.

It's a head scratcher what the philosophical reticence is for completing the picture with a

  submission_relay_inet_protocols

or somesuch.

> Postfix added support for IPv6 back in version 2 days.
> 
>     inet_protocols = ipv4, ipv6
> 
> or
> 
>     inet_protocols = all
> 
> (My ISP does not provide IPv6, so I have little experience with it, so entirely possible I am missing something here).
> 
>