Force IPv4 when sending to gmail

Because Free does not provide rDNS on IPv6
so GMail complains that it does not find a PTR record
for our IPv6 address

cluster/prod/app/email/config/postfix/master.cf

@@ -19,11 +19,6 @@ smtps      inet  n       -       n       -       -       smtpd
     -o smtpd_sasl_auth_enable=yes
     -o smtpd_client_restrictions=permit_sasl_authenticated,reject
     -o milter_macro_daemon_name=ORIGINATING
-slow unix       -       -      n        -       5       smtp
-  -o syslog_name=postfix-slow
-  -o smtp_destination_concurrency_limit=3
-  -o slow_destination_rate_delay=1
-
 
 #628       inet  n       -       -       -       -       qmqpd
 pickup     fifo  n       -       n       60      1       pickup
@@ -42,6 +37,14 @@ proxywrite unix -       -       n       -       1       proxymap
 # When relaying mail as backup MX, disable fallback_relay to avoid MX loops
 smtp       unix  -       -       n       -       -       smtp
 #       -o smtp_helo_timeout=5 -o smtp_connect_timeout=5
+
+smtp-ipv4  unix  -       -       n       -       -       smtp
+    -o syslog_name=postfix-ipv4
+    -o inet_protocols=ipv4 
+slow  unix       -       -       n       -       5       smtp
+    -o syslog_name=postfix-slow
+    -o smtp_destination_concurrency_limit=3
+    -o slow_destination_rate_delay=1
 relay      unix  -       -       n       -       -       smtp
     -o smtp_fallback_relay=
 showq      unix  n       -       n       -       -       showq

cluster/prod/app/email/config/postfix/transport

@@ -3,3 +3,4 @@
 #orange.com slow:
 #orange.fr slow:
 #smtp.orange.fr slow:
+gmail.com smtp-ipv4: