diff -drup a/includes/base.inc b/includes/base.inc
--- a/includes/base.inc	Mon Jan 21 22:37:24 2013
+++ b/includes/base.inc	Mon Jan 28 13:55:13 2013
@@ -330,6 +330,9 @@ abstract class MigrationBase {
         $conf['mail_system'][$system] = 'MigrateMailIgnore';
       }
     }
+	else {
+	  $conf['mail_system']['default-system'] = 'MigrateMailIgnore';
+	}
 
     // Make sure we clear our semaphores in case of abrupt exit
     register_shutdown_function(array($this, 'endProcess'));