feat(amavis): Don't allow user to send spam/virus

With this configuration if the user attempts to send spam or a
virus, the message will be quarantined and the user will be
notified of the issue.

MR !9

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

@@ -4,5 +4,7 @@ $interface_policy{'10023'} = 'SUBMISSION';
 $policy_bank{'SUBMISSION'} = {
     originating => 1,
     smtpd_discard_ehlo_keywords => ['8BITMIME'],
+    final_spam_destiny => D_BOUNCE, # Bounce so user is notified
+    final_virus_destiny => D_BOUNCE, # Bounce so user is notified
 };