fix(Mail): prevent sending email for out-of-stock products

classes/Mail.php

@@ -151,6 +151,9 @@ class MailCore extends ObjectModel
             $idShop = Context::getContext()->shop->id;
         }
 
+        if ( $template == 'productoutofstock' )
+          return false;
+
         $hookBeforeEmailResult = Hook::exec(
             'actionEmailSendBefore',
             [