diff --git a/core/Email.php b/core/Email.php
index c1248de36..8756f7b25 100755
--- a/core/Email.php
+++ b/core/Email.php
@@ -2,6 +2,7 @@
 
 define('X_MAILER', 'SilverStripe Mailer - version 2006.06.21 (Sent from "'.$_SERVER['SERVER_NAME'].'")');
 
+// Note: The constant 'BOUNCE_EMAIL' should be defined as a valid email address for where bounces should be returned to.
 /**
  * Class to support sending emails.
  */