fix: Move spam to mailbox associated to the \Junk special-use attribute (#3925)

Co-authored-by: Brennan Kinney <5098581+polarathene@users.noreply.github.com>

test/config/junk-mailbox/user-patches.sh

@@ -0,0 +1,21 @@
+#!/bin/bash
+##
+# This user script will be executed between configuration and starting daemons
+# To enable it you must save it in your config directory as "user-patches.sh"
+##
+
+echo "[user-patches.sh] Adjusting 'Junk' mailbox name to verify delivery to Junk mailbox based on special-use flag instead of mailbox's name"
+
+sed -i -e 's/mailbox Junk/mailbox Spam/' /etc/dovecot/conf.d/15-mailboxes.conf
+
+### Before / After ###
+
+# mailbox Junk {
+#   auto = subscribe
+#   special_use = \Junk
+# }
+
+# mailbox Spam {
+#   auto = subscribe
+#   special_use = \Junk
+# }