Mention smtp ports 587 and 465 in config template

config/main.inc.php.dist

@@ -134,7 +134,8 @@ $rcmail_config['messages_cache'] = false;
 // For example %n = mail.domain.tld, %d = domain.tld
 $rcmail_config['smtp_server'] = '';
 
-// SMTP port (default is 25; 465 for SSL)
+// SMTP port (default is 25; use 587 for STARTTLS or 465 for the
+// deprecated SSL over SMTP (aka SMTPS))
 $rcmail_config['smtp_port'] = 25;
 
 // SMTP username (if required) if you use %u as the username Roundcube