diff --git a/main.cf.insert b/main.cf.insert
index 829788f..2c879cb 100644
--- a/main.cf.insert
+++ b/main.cf.insert
@@ -14,7 +14,7 @@ relayhost = [{SMARTHOST}]:{SMARTHOST_PORT}
 #smtpd_tls_chain_files = /certs/privkey.pem, /certs/fullchain.pem
 #smtpd_tls_mandatory_ciphers = high
 #smtpd_tls_mandatory_exclude_ciphers = aNULL, MD5
-#smtpd_tls_mandatory_protocols = >=TLSv1.2
+#smtpd_tls_mandatory_protocols = >=TLSv1.2, <=TLSv1.3
 #smtpd_tls_security_level = {LOCAL_ENCRYPTION}
 
 smtp_tls_security_level = {SMARTHOST_ENCRYPTION}