Do not log specific errors

Sources/Subs-Post.php

@@ -1592,10 +1592,17 @@ function server_parse($message, $socket, $code, &$response = null)
  if ($code === null)
  return substr($server_response, 0, 3);
 
- if (($server_code = substr($server_response, 0, 3)) != $code)
- {
- if ($server_code < 500 && !in_array($server_code, [450, 451, 421]))
+ $resonse_code = (int) substr($server_response, 0, 3);
+ if ($resonse_code != $code)
+ {
+ // Ignoreable errors that we can't fix should not be logged.
+ /*
+ * 550 - cPanel rejected sending due to DNS issues
+ * 450 - DNS Routing issues
+ */
+ if ($resonse_code < 500 && !in_array($resonse_code, [450]))
  log_error($txt['smtp_error'] . $server_response);
+
  return false;
  }