diff --git a/lib/moodlelib.php b/lib/moodlelib.php
index 25e51ea9f94..6326937b1d3 100644
--- a/lib/moodlelib.php
+++ b/lib/moodlelib.php
@@ -5800,23 +5800,22 @@ function email_to_user($user, $from, $subject, $messagetext, $messagehtml = '',
 
     if (!validate_email($user->email)) {
         // We can not send emails to invalid addresses - it might create security issue or confuse the mailer.
-        $invalidemail = "User $user->id (".fullname($user).") email ($user->email) is invalid! Not sending.";
-        error_log($invalidemail);
-        if (CLI_SCRIPT) {
-            mtrace('Error: lib/moodlelib.php email_to_user(): '.$invalidemail);
-        }
+        debugging("email_to_user: User $user->id (".fullname($user).") email ($user->email) is invalid! Not sending.");
         return false;
     }
 
     if (over_bounce_threshold($user)) {
-        $bouncemsg = "User $user->id (".fullname($user).") is over bounce threshold! Not sending.";
-        error_log($bouncemsg);
-        if (CLI_SCRIPT) {
-            mtrace('Error: lib/moodlelib.php email_to_user(): '.$bouncemsg);
-        }
+        debugging("email_to_user: User $user->id (".fullname($user).") is over bounce threshold! Not sending.");
         return false;
     }
 
+    // TLD .invalid  is specifically reserved for invalid domain names.
+    // For More information, see {@link http://tools.ietf.org/html/rfc2606#section-2}.
+    if (substr($user->email, -8) == '.invalid') {
+        debugging("email_to_user: User $user->id (".fullname($user).") email domain ($user->email) is invalid! Not sending.");
+        return true; // This is not an error.
+    }
+
     // If the user is a remote mnet user, parse the email text for URL to the
     // wwwroot and modify the url to direct the user's browser to login at their
     // home site (identity provider - idp) before hitting the link itself.