diff --git a/php/src/mail/mailer.php b/php/src/mail/mailer.php
index b19e2bc..d11eb34 100644
--- a/php/src/mail/mailer.php
+++ b/php/src/mail/mailer.php
@@ -21,6 +21,7 @@ class mailer {
       return true;
     } else {
       switch (strval($value)) {
+      case "":
       case "0":
       case "no":
       case "off":