diff --git a/en_US/howto/manage.iredapd.md b/en_US/howto/manage.iredapd.md
index f26470dd..4c01ee09 100644
--- a/en_US/howto/manage.iredapd.md
+++ b/en_US/howto/manage.iredapd.md
@@ -133,6 +133,8 @@ White/blacklisting is controlled by plugin `amavisd_wblist` (file
 
 ## Greylisting
 
+For technical details about greylisting, please visit <http://greylisting.org/>
+
 ### How to disable greylisting completely
 
 To disable greylisting completely, please remove plugin name `greylisting`
diff --git a/html/manage.iredapd.html b/html/manage.iredapd.html
index 97da6bfa..0756ec30 100644
--- a/html/manage.iredapd.html
+++ b/html/manage.iredapd.html
@@ -151,6 +151,7 @@ parameter <code>plugins =</code>:</p>
 </code></pre>
 
 <h2 id="greylisting">Greylisting</h2>
+<p>For technical details about greylisting, please visit <a href="http://greylisting.org/">http://greylisting.org/</a></p>
 <h3 id="how-to-disable-greylisting-completely">How to disable greylisting completely</h3>
 <p>To disable greylisting completely, please remove plugin name <code>greylisting</code>
 in iRedAPD config file <code>/opt/iredapd/settings.py</code>, parameter <code>plugins =</code>:</p>