폼메일이 발송이 안되네요.. 왜 그럴까요? 채택완료

<meta charset="utf-8"><?phpif(isset($_POST['telephone'])) {         	$email_to = "---@naver.com";	$email_subject = "[폼메일] 견적의뢰 문의사항입니다.";	$email_subject = '=?UTF-8?B?'.base64_encode($email_subject).'?=';               function died($error) {        // your error code can go here        echo "<script> alert('메일발송을 실패하였습니다.\\n이메일 및 연락처를 정확히 입력해주세요.');";		echo "history.go(-1);";		echo "</script>";        die();    }         // validation expected data exists    if( !isset($_POST['telephone'])) {        died('We are sorry, but there appears to be a problem with the form you submitted.');           }         $telephone = $_POST['telephone']; // not required         $error_message = "";      if(strlen($telephone) < 2) {    $error_message .= 'The Comments you entered do not appear to be valid.<br />';  }  if(strlen($error_message) > 0) {    died($error_message);  }    $email_message = "";         function clean_string($string) {      $bad = array("content-type","bcc:","to:","cc:","href");      return str_replace($bad,"",$string);    }         $email_message .= "연락처 : ".clean_string($telephone)."\n\n";          // create email headers$headers = 'From: '.$email_from;// 제목이 깨질경우 아래 캐릭터셋 적용 @mail($email_to, $email_subject, $email_message, $headers);  ?> <!-- include your own success html here --> <script>alert ("메일이 발송되었습니다.\n빠른 시일안에 답변드리겠습니다.");location.href="http://---.com/";</script> <?php}?>