diff --git a/includes/simplenews.mail.inc b/includes/simplenews.mail.inc
index f3eaede..4cc44d9 100644
--- a/includes/simplenews.mail.inc
+++ b/includes/simplenews.mail.inc
@@ -214,6 +214,12 @@ function simplenews_send_source(SimplenewsSourceInterface $source) {
  * @ingroup spool
  */
 function simplenews_mail_spool($limit = SIMPLENEWS_UNLIMITED, array $conditions = array()) {
+
+  // Ensure lock available on mail spool process
+  if (!lock_acquire('simplenews_mail_spool')) {
+    return FALSE;
+  }
+
   $check_counter = 0;
 
   // Send pending messages from database cache.
@@ -309,8 +315,11 @@ function simplenews_mail_spool($limit = SIMPLENEWS_UNLIMITED, array $conditions
     variable_set('simplenews_last_sent', $count_success);
 
     simplenews_revert_user();
+    lock_release('simplenews_mail_spool');
     return $count_success;
   }
+  // Release lock
+  lock_release('simplenews_mail_spool');
 }
 
 /**
diff --git a/simplenews_rules/simplenews_rules.rules.inc b/simplenews_rules/simplenews_rules.rules.inc
index d4c9086..bbe0fbf 100755
--- a/simplenews_rules/simplenews_rules.rules.inc
+++ b/simplenews_rules/simplenews_rules.rules.inc
@@ -229,7 +229,10 @@ function simplenews_rules_action_unsubscribe($args, $settings) {
  */
 function simplenews_rules_action_subscription_delete($args, $settings) {
   if (!empty($args['mail']) && !empty($args['tid'])){
-    simplenews_subscription_delete(array('mail' => $args['mail'], 'tid' => $args['tid']));
+    $subscriber = simplenews_subscriber_load_by_mail($args['mail']);
+    if ($subscriber) {
+      simplenews_subscription_delete(array('snid' => $subscriber->snid, 'tid' => $args['tid']));
+    }
   }
 }