Subject: Disable local real root

Avoid denial-of-service by filling up root space with unattended messages.

Index: exim4-4.89/debian/debconf/conf.d/router/300_exim4-config_real_local
===================================================================
--- exim4-4.89.orig/debian/debconf/conf.d/router/300_exim4-config_real_local
+++ exim4-4.89/debian/debconf/conf.d/router/300_exim4-config_real_local
@@ -18,5 +18,6 @@ real_local:
   condition = COND_LOCAL_SUBMITTER
   local_part_prefix = real-
   check_local_user
+  local_parts = ! root
   transport = LOCAL_DELIVERY