เกี่ยวกับส่งเมลล์ค่ะช่วยหน่อยนะค่ะ ทำยังไงมานก็ขึ้น This user does not exist in the system.

   <?php 
			$user_forget=$_POST[user_forget];
			
			if ($user_forget==""){
			echo "<h3>ERROR : Please input your Username</h3>"; exit();
			}
			include "connect.php";
			 $sql = "select admin_username from admin WHERE admin_username='$user_forget'";
			 $result = mysql_db_query($dbname,$sql);	
			$record = mysql_fetch_array($result); 
			$num=mysql_num_rows($result);
			$to=$record[admin_email];
			$password=$record[admin_password];
			if (num<=0){
		echo "<h3>ERROR : This user does not exist in the system.</h3>";
		} else {
			$subject = "Inform the membership password.";
			$message = "Username : $user_forget </br>Password : $admin_password";
			$headers = "From IMSDC";
							if (mail($to, $subject, $message, $header)) {
								echo "<h3>Password mainly sent successfully.</h3>";
							}else{ echo "<h3>Cannot  sent password to email </h3>";}
			}
   			mysql_close(); 
			?>