Problem sending e-mail with php

I have a problem with my email sending code it works normally but my email arrives unformatted and showing the tags of html follows my code

HTML

<form id="form-elements" onSubmit="return false">
                        <div class="row">
                            <div class="col-md-12 center">
                                <div id="result"></div>
                            </div>
                        </div>

                        <div class="row">
                            <div class="col-sm-4">
                                <div class="form-group">
                                    <input type="text" class="form-control" placeholder="Nome" name="name"
                                           id="name" required></div>
                            </div>
                            <div class="col-sm-4">
                                <div class="form-group">
                                    <input type="email" class="form-control" placeholder="E-mail" name="email"
                                           id="email" required></div>
                            </div>
                            <div class="col-sm-4">
                                <div class="form-group">
                                    <input type="text" class="form-control" placeholder="Telefone" name="phone"
                                           id="phone" required>
                                </div>
                            </div>
                            <div class="col-xs-12">
                                <textarea id="input" class="form-control" rows="7" required="required"
                                          placeholder="Mensagem" name="message" id="message"></textarea>
                            </div>
                            <button type="submit" class="btn btn-default buttons" id="submit_btn">Enviar</button>
                        </div>
                    </form>

PHP

<?php
if($_POST)
{
    $to_Email       = "[email protected]"; //Replace with recipient email address
    $subject        = 'TW Acessoria - Novo contato do site'; //Subject line for emails


    //check if its an ajax request, exit if not
    if(!isset($_SERVER['HTTP_X_REQUESTED_WITH']) AND strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) != 'xmlhttprequest') {

        //exit script outputting json data
        $output = json_encode(
        array(
            'type'=>'error',
            'text' => 'Request must come from Ajax'
        ));

        die($output);
    }

    //check $_POST vars are set, exit if any missing
    if(!isset($_POST["userName"]) || !isset($_POST["userEmail"]) || !isset($_POST["userMessage"]))
    {
        $output = json_encode(array('type'=>'error', 'text' => 'Os campos de entrada estão vazios!  '));
        die($output);
    }

    //Sanitize input data using PHP filter_var().
    $user_Name        = filter_var($_POST["userName"], FILTER_SANITIZE_STRING);
    $user_Email       = filter_var($_POST["userEmail"], FILTER_SANITIZE_EMAIL);
    $user_Phone = $_POST["userTelephone"];
    $user_Message     = filter_var($_POST["userMessage"], FILTER_SANITIZE_STRING);

    //additional php validation
    if(strlen($user_Name)<3) // If length is less than 3 it will throw an HTTP error.
    {
        $output = json_encode(array('type'=>'error', 'text' => 'O campo nome não pode ficar vazio'));
        die($output);
    }
    if(!filter_var($user_Email, FILTER_VALIDATE_EMAIL)) //email validation
    {
        $output = json_encode(array('type'=>'error', 'text' => 'Por favor ultilize um e-mail válido'));
        die($output);
    }

    if(strlen($user_Message)<5) //check emtpy message
    {
        $output = json_encode(array('type'=>'error', 'text' => 'Por favor insira uma mensagem'));
        die($output);
    }


    $message_Body = "<strong>Name: </strong>". $user_Name ."<br>";
    $message_Body .= "<strong>Email: </strong>". $user_Email ."<br>";
    $message_Body .= "<strong>Phone: </strong>". $user_Phone ."<br>";
    $message_Body .= "<strong>Message: </strong>". $user_Message ."<br>";



    $headers = "From: " . strip_tags($user_Email) . "\r\n";
    $headers .= "Reply-To: ". strip_tags($user_Email) . "\r\n";
    $headers .= "MIME-Version: 1.0\r\n";
    $headers .= "Content-Type: text/html; charset=ISO-8859-1\r\n";



    //proceed with PHP email.
    $headers = 'From: '.$user_Email.'' . "\r\n" .
    'Reply-To: '.$user_Email.'' . "\r\n" .
    'X-Mailer: PHP/' . phpversion();



    $sentMail = @mail($to_Email, $subject, $message_Body, $headers);

    if(!$sentMail)
    {
        $output = json_encode(array('type'=>'error', 'text' => 'Ocorreu um erro tente novamente'));
        die($output);
    }else{
        $output = json_encode(array('type'=>'message', 'text' => 'Olá '.$user_Name .'Obrigado pelo seu contato retornaremos em breve.'));
        die($output);
    }
}
?>

JS

  $("#submit_btn").click(function() {
                //get input field values
                var user_name       = $('input[name=name]').val();
                var user_email      = $('input[name=email]').val();
                var user_telephone      = $('input[name=phone]').val();
                var user_message    = $('textarea[name=message]').val();

                //simple validation at client's end
                var post_data, output;
                var proceed = true;
                if(user_name==""){
                        proceed = false;
                }
                if(user_email==""){
                        proceed = false;
                }
                if(user_message=="") {
                        proceed = false;
                }

                //everything looks good! proceed...
                if(proceed)
                {
                        //data to be sent to server
                        post_data = {'userName':user_name, 'userEmail':user_email, 'userTelephone':user_telephone, 'userMessage':user_message};

                        //Ajax post data to server
                        $.post('contact.php', post_data, function(response){

                                //load json data from server and output message
                if(response.type == 'error')
                {
                    output = '<div class="alert-danger" style="padding:10px; margin-bottom:25px;">'+response.text+'</div>';
                }else{
                    output = '<div class="alert-success" style="padding:10px; margin-bottom:25px;">'+response.text+'</div>';

                    //reset values in all input fields
                    $('#form-elements input').val('');
                    $('#form-elements textarea').val('');
                }

                $("#result").hide().html(output).slideDown();
                        }, 'json');

                }
        });

        //reset previously set border colors and hide all message on .keyup()
        $("#form-elements input, #form-elements textarea").keyup(function() {
                $("#result").slideUp();
        });

This is the way that email arrives