backport fix for #474 to 1.5

core/dovecot/sieve/report-ham.sieve

@@ -1,3 +1,11 @@
-require "vnd.dovecot.execute";
+require ["vnd.dovecot.execute", "copy", "imapsieve", "environment", "variables"];
+
+if environment :matches "imap.mailbox" "*" {
+  set "mailbox" "${1}";
+}
+
+if string "${mailbox}" "Trash" {
+  stop;
+}
 
 execute :pipe "mailtrain" "ham";