diff --git a/lib/moodlelib.php b/lib/moodlelib.php
index 73d9c9a8064..400434dbd8a 100644
--- a/lib/moodlelib.php
+++ b/lib/moodlelib.php
@@ -4069,7 +4069,7 @@ function email_is_not_allowed($email) {
             if (!$allowedpattern) {
                 continue;
             }
-            if (strpos($email, $allowedpattern) !== false) {  // Match!
+            if (strpos(strrev($email), strrev($allowedpattern)) === 0) { // Match!   (bug 5250)
                 return false;
             }
         }
@@ -4082,7 +4082,7 @@ function email_is_not_allowed($email) {
             if (!$deniedpattern) {
                 continue;
             }
-            if (strpos($email, $deniedpattern) !== false) {   // Match!
+            if (strpos(strrev($email), strrev($deniedpattern)) === 0) { // Match!   (bug 5250)
                 return get_string('emailnotallowed', '', $CFG->denyemailaddresses);
             }
         }