Need Help with Contact Form and Newsletter

<h2>Contact Form</h2>
                            <form method="POST" name="contact_form"
                            action="contact.php">
                            <p>
                            <label for='name'>Name: </label><br>
                            <input type="text" name="name">
                            </p>
                            <p>
                            <label for='email'>Email: </label><br>
                            <input type="text" name="email">
                            </p>
                            <p>
                            <label for='message'>Message:</label> <br>
                            <textarea name="message"></textarea>
                            </p>
                            <p>
                            <img src="captcha_code_file.php?rand=<?php echo rand(); ?>" id='captchaimg' ><br>
                            <label for='message'>Enter the code above here :</label><br>
                            <input id="6_letters_code" name="6_letters_code" type="text"><br>
                            <small>Can't read the image? click <a href='javascript: refreshCaptcha();'>here</a> to refresh</small>
                            </p>
                            <input type="submit" value="Submit" name='submit'>
                            </form>
                            <script language="JavaScript">
                            // Code for validating the form
                            var frmvalidator = new Validator("contact_form");
                            //remove the following two lines if you like error message box popups
                            frmvalidator.EnableOnPageErrorDisplaySingleBox();
                            frmvalidator.EnableMsgsTogether();
                            
                            frmvalidator.addValidation("name","req","Please provide your name");
                            frmvalidator.addValidation("email","req","Please provide your email");
                            frmvalidator.addValidation("email","email","Please enter a valid email address");
                            </script>
                            <script language='JavaScript' type='text/javascript'>
                            function refreshCaptcha()
                            {
                                var img = document.images['captchaimg'];
                                img.src = img.src.substring(0,img.src.lastIndexOf("?"))+"?rand="+Math.random()*1000;
                            }
                            </script>

<?php
$your_email ='';// <<=== update to your email address

session_start();
$errors = '';
$name = '';
$visitor_email = '';
$user_message = '';

if(isset($_POST['submit']))
{
    
    $name = $_POST['name'];
    $visitor_email = $_POST['email'];
    $user_message = $_POST['message'];
    ///------------Do Validations-------------
    if(empty($name)||empty($visitor_email))
    {
        $errors .= "\n Name and Email are required fields. ";    
    }
    if(IsInjected($visitor_email))
    {
        $errors .= "\n Bad email value!";
    }
    if(empty($_SESSION['6_letters_code'] ) ||
     strcasecmp($_SESSION['6_letters_code'], $_POST['6_letters_code']) != 0)
    {
    //Note: the captcha code is compared case insensitively.
    //if you want case sensitive match, update the check above to
    // strcmp()
        $errors .= "\n The captcha code does not match!";
    }
    
    if(empty($errors))
    {
        //send the email
        $to = $your_email;
        $subject="New form submission";
        $from = $your_email;
        $ip = isset($_SERVER['REMOTE_ADDR']) ? $_SERVER['REMOTE_ADDR'] : '';
        
        $body = "A user $name submitted the contact form:\n".
        "Name: $name\n".
        "Email: $visitor_email \n".
        "Message: \n ".
        "$user_message\n".
        "IP: $ip\n";    
        
        $headers = "From: $from \r\n";
        $headers .= "Reply-To: $visitor_email \r\n";
        
        mail($to, $subject, $body,$headers);
        
        header('Location: contacts.html');
    }
}

// Function to validate against any email injection attempts
function IsInjected($str)
{
 $injections = array('(\n+)',
       '(\r+)',
       '(\t+)',
       '(%0A+)',
       '(%0D+)',
       '(%08+)',
       '(%09+)'
       );
 $inject = join('|', $injections);
 $inject = "/$inject/i";
 if(preg_match($inject,$str))
  {
  return true;
 }
 else
  {
  return false;
 }
}
?>
<?php
if(!empty($errors)){
echo "<p class='err'>".nl2br($errors)."</p>";
}
?>