diff --git a/testsite/tls/templates/mail.example.com_smtp.cfg b/testsite/tls/templates/mail.example.com_smtp.cfg
index 5910ad13a5a88ef1383f89721d58913e38309a43..4a32651b000f27e57878864024f919da0cae09c2 100644
--- a/testsite/tls/templates/mail.example.com_smtp.cfg
+++ b/testsite/tls/templates/mail.example.com_smtp.cfg
@@ -25,3 +25,8 @@ tls_www_server
 # Whether this certificate will be used to sign data (needed
 # in TLS DHE ciphersuites).
 signing_key
+
+# Whether this certificate will be used to encrypt data (needed
+# in TLS RSA ciphersuites). Note that it is preferred to use different
+# keys for encryption and signing.
+encryption_key