feat(amavis): don't allow user to send banned email

This configuration blocks the user from sending an email that w
would otherwise be blocked. in this instance the user is notified.

MR !9

include/etc/amavis/conf.d/60-policy-bank-submission

@@ -4,6 +4,7 @@ $interface_policy{'10023'} = 'SUBMISSION';
 $policy_bank{'SUBMISSION'} = {
     originating => 1,
     smtpd_discard_ehlo_keywords => ['8BITMIME'],
+    final_banned_destiny => D_BOUNCE, # Bounce so user is notified
     final_spam_destiny => D_BOUNCE, # Bounce so user is notified
     final_virus_destiny => D_BOUNCE, # Bounce so user is notified
 };