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]

my server is a linux, dual-stack IPv4/IPv6 host

it runs multiple services, including, but not limited to, postfix & dovecot

the hostname is

	internal.mx.example.com

its DNS config,

	host internal.mx.example.com
		internal.mx.example.com has address 10.1.1.15
		internal.mx.example.com has IPv6 address fd80:10:1::15
		internal.mx.example.com mail is handled by 5 internal.mx.example.com.

here, for dovecot

	dovecot --version
		2.3.13 (89f716dc2)

submission is configured to relay to the same-host postfix instance, listening @ port 465

	./conf.d/10-master.conf
		...
		protocols = imap submission lmtp sieve
		...
		submission_relay_host       = internal.mx.example.com
		submission_relay_port       = 465
		submission_relay_ssl        = smtps
		submission_relay_ssl_verify = yes
		submission_relay_trusted    = yes

whereas other services listen at both IPv4 & IPv6 addresses, with IPv6 preferred over IPv4, postfix listens ONLY on IPv4,

	postconf inet_protocols
		inet_protocols = ipv4

and, as intended, simply refuses ipv6 connections

	telnet 10.1.1.15 465
		Trying 10.1.1.15...
		Connected to 10.1.1.15.
		Escape character is '^]'.
		^]
		telnet> quit
		Connection closed.

	telnet -6 fd80:10:1::15 465
		Trying fd80:10:1::15...
		telnet: connect to address fd80:10:1::15: Connection refused

on each/every mail submit -- via dovecot -- dovecot makes the connection

	2021-04-03 19:35:35 submission(mailer at mx.example.com)</tnO6xm/PIqsHgsH>: Debug: smtp-server: conn 10.1.2.163:35388 [1]: Server accepted connection (fd=7)
	2021-04-03 19:35:35 submission(mailer at mx.example.com)</tnO6xm/PIqsHgsH>: Debug: smtp-server: conn 10.1.2.163:35388 [1]: Connection created
	2021-04-03 19:35:35 submission(mailer at mx.example.com)</tnO6xm/PIqsHgsH>: Debug: smtp-client: conn internal.mx.example.com:465 [1]: Connection created
	2021-04-03 19:35:35 submission(mailer at mx.example.com)</tnO6xm/PIqsHgsH>: Debug: smtp-client: conn internal.mx.example.com:465 [1]: Disconnected

looks up IP address

	2021-04-03 19:35:35 submission(mailer at mx.example.com)</tnO6xm/PIqsHgsH>: Debug: smtp-client: conn internal.mx.example.com:465 [1]: Looking up IP address
	2021-04-03 19:35:35 submission(mailer at mx.example.com)</tnO6xm/PIqsHgsH>: Debug: smtp-client: conn internal.mx.example.com:465 [1]: Performing asynchronous DNS lookup
	2021-04-03 19:35:35 submission(mailer at mx.example.com)</tnO6xm/PIqsHgsH>: Debug: smtp-server: conn 10.1.2.163:35388 [1]: Sent: 235 2.7.0 Logged in.

finds BOTH IPs -- IPv4 & IPv6

	2021-04-03 19:35:35 submission(mailer at mx.example.com)</tnO6xm/PIqsHgsH>: Debug: smtp-client: conn internal.mx.example.com:465 [1]: DNS lookup successful; got 2 IPs

then first tries to connect via the host's IPv6 address,

	2021-04-03 19:35:35 submission(mailer at mx.example.com)</tnO6xm/PIqsHgsH>: Debug: smtp-client: conn internal.mx.example.com:465 [1]: Connecting to fd80:10:1::15:465
	2021-04-03 19:35:35 submission(mailer at mx.example.com)</tnO6xm/PIqsHgsH>: Debug: smtp-client: conn internal.mx.example.com:465 ([fd80:10:1::15]:465) [1]: Connecting
	2021-04-03 19:35:35 submission(mailer at mx.example.com)</tnO6xm/PIqsHgsH>: Debug: smtp-client: conn internal.mx.example.com:465 ([fd80:10:1::15]:465) [1]: Waiting for connect (fd=8) to finish for max 0 msecs

############
   FAILS
############

	2021-04-03 19:35:35 submission(mailer at mx.example.com)</tnO6xm/PIqsHgsH>: Debug: smtp-client: conn internal.mx.example.com:465 ([fd80:10:1::15]:465) [1]: Client connection failed (fd=8)

then proceeds to connect to the host's IPv4 address

	2021-04-03 19:35:35 submission(mailer at mx.example.com)</tnO6xm/PIqsHgsH>: Debug: smtp-client: conn internal.mx.example.com:465 ([fd80:10:1::15]:465) [1]: Connecting to 10.1.1.15:465
	2021-04-03 19:35:35 submission(mailer at mx.example.com)</tnO6xm/PIqsHgsH>: Debug: smtp-client: conn internal.mx.example.com:465 (10.1.1.15:465) [1]: Connecting
	2021-04-03 19:35:35 submission(mailer at mx.example.com)</tnO6xm/PIqsHgsH>: Debug: smtp-client: conn internal.mx.example.com:465 (10.1.1.15:465) [1]: Waiting for connect (fd=11) to finish for max 0 msecs
	2021-04-03 19:35:35 submission(mailer at mx.example.com)</tnO6xm/PIqsHgsH>: Debug: smtp-client: conn internal.mx.example.com:465 (10.1.1.15:465) [1]: Client connected (fd=11)
	2021-04-03 19:35:35 submission(mailer at mx.example.com)</tnO6xm/PIqsHgsH>: Debug: smtp-client: conn internal.mx.example.com:465 (10.1.1.15:465) [1]: Connected to server (from 10.1.1.15:52880)
	2021-04-03 19:35:35 submission(mailer at mx.example.com)</tnO6xm/PIqsHgsH>: Debug: smtp-client: conn internal.mx.example.com:465 (10.1.1.15:465) [1]: Starting SSL handshake
	2021-04-03 19:35:35 submission(mailer at mx.example.com)</tnO6xm/PIqsHgsH>: Debug: smtp-client: conn internal.mx.example.com:465 (10.1.1.15:465) [1]: SSL handshake successful
	...

and submission continues/completes


I need to get Dovecot to stop trying/failing @ those IPv6 address submission connections.

Either by

	(1) trying IPv4 *first*, before IPv6, to avoid the FAIL on submission

or

	(2) turning off submission relay by IPv6 altogether, as I'll never use it

What's the config required to do either/both?