diff --git a/ndncert-mail.conf.sample b/ndncert-mail.conf.sample
index 48e31b1..7731cf5 100644
--- a/ndncert-mail.conf.sample
+++ b/ndncert-mail.conf.sample
@@ -1,7 +1,7 @@
 [ndncert.smtp]
 SMTP_SERVER = localhost or remote smtp server
 SMTP_PORT = port number, usually one from 25 465 587
-ENCRYPT_MODE = select one from ssl/tls/none
+ENCRYPT_MODE = select one from ssl/starttls/none
 SMTP_USER = leave it empty if you do not have one
 SMTP_PASSWORD = leave it empty if you do not have one
 
diff --git a/ndncert-send-email-challenge.py b/ndncert-send-email-challenge.py
index 56d8bbe..a220f92 100755
--- a/ndncert-send-email-challenge.py
+++ b/ndncert-send-email-challenge.py
@@ -40,7 +40,7 @@
 # connect to SMTP server
 if encrypt_mode == 'ssl':
     context = smtplib.SMTP_SSL(server, port, timeout=10)
-elif encrypt_mode == 'tls':
+elif encrypt_mode == 'starttls':
     context = smtplib.SMTP(server, port, timeout=10)
     context.starttls()
 elif encrypt_mode == 'none':