install_postfix_: add section for (commented) parameter 'smtp_address_preference'.

install_postfix_advanced.sh

@@ -1185,6 +1185,12 @@ mynetworks =
 smtp_bind_address = $IPV4
 smtp_bind_address6 = $IPV6
 
+# The address type ("ipv6", "ipv4" or "any") that the Postfix SMTP client will try first,
+# when a destination has IPv6 and IPv4 addresses with equal MX preference. This feature
+# has no effect unless the inet_protocols setting enables both IPv4 and IPv6.
+#
+#smtp_address_preference = ipv4
+
 EOF
 else
    cat <<EOF >> /etc/postfix/main.cf