Do not fold lookup tables to lowercase

This behavior is undesirable in our case since it prevents users with
uppercase letters in their username from receiving email

site_postfix/manifests/init.pp

@@ -50,7 +50,7 @@ class site_postfix (
   }
 
   exec { 'postmap_build':
-    command     => '/usr/sbin/postmap /etc/postfix/virtual',
+    command     => '/usr/sbin/postmap -f /etc/postfix/virtual',
     refreshonly => true,
     notify      => Service['postfix'],
   }