[Dovecot] New global post-filter: drop duplicates as received within 60 minutes

data/conf/dovecot/global_sieve_after

@@ -6,6 +6,7 @@ require "mailbox";
 require "variables";
 require "subaddress";
 require "envelope";
+require "duplicate";
 
 if header :contains "X-Spam-Flag" "YES" {
   fileinto "Junk";
@@ -22,3 +23,8 @@ if allof (
     fileinto :create "INBOX/${tag}";
   }
 }
+
+if duplicate {
+  discard;
+  stop;
+}

data/web/inc/lib/sieve/extensions/duplicate.xml

@@ -0,0 +1,9 @@
+<?xml version='1.0' standalone='yes'?>
+
+<extension name="duplicate">
+
+	<test name="duplicate">
+
+	</test>
+
+</extension>