how to set smtp-client -> submission_relay_host for IPv4 only?

[PGNet Dev]

On 10/15/20 2:02 PM, jeremy ardley wrote:
>> how/where do I configure (just) the dovecot smtp-client -> submission_relay_host to only connect IPv4?
> 
> It appears your host has A and AAAA records in your DNS. The clients will try IPV6 first if they see an AAAA record.
> 
> If you don't need IPV6 for your host remove the AAAA record. All connections will then only use IPV4.
> 
> If you need IPV6 for some other reason then create an alias DNS A record and point your clients to that instead

That's not the issue.

All my machines are dual stack.
All my hosts' DNS records exist for both A & AAAA records.

Some services listen on only IPv4, some only on IPv6, some both.

For Dovecot _listeners_ it's trivial to set IPv4/6-only, or both, addresses.

It's also trivial to set OTHER clients, connecting TO Dovecot, to use IPv4-only.

I'm asking how/where to 'tell', via config, Dovecot's smtp-CLIENT, that's making to connection to the submission_relay_host, to use _only_ IPv4.