diff --git a/docs/usage.rst b/docs/usage.rst
index 7fbc540568b06dc1977cab73ea2bcbb6911318dc..3defa3f95c1835a717807585e4202a293863430c 100644
--- a/docs/usage.rst
+++ b/docs/usage.rst
@@ -982,7 +982,11 @@ external addresses on those two servers goes through our anti-virus scanner.
    :file:`~/mysite/group_vars/all.yml`
    ::
 
-      # First, let's make sure any mails directed to localhost root account get
+      # Define what X.509 certificates should be used for validating
+      # the certificate of server we are relaying the mails through.
+      smtp_relay_truststore: "{{ lookup('file', '~/mysite/tls/truststore.pem') }}"
+
+      # Make sure any mails directed to localhost root account get
       # forwarded to one of our mail users as well.
       local_mail_aliases:
         root: root john.doe@example.com