<form action="" method="POST">
                        <ul class="form-style-1">
                            <li>
                                <input type="text" id="mail-name" name="name" class="field-divided" maxlength="15"  placeholder="Voornaam *" />&nbsp;<input type="text" id="mail-lastname" name="lastname" class="field-divided" maxlength="15" placeholder="Achternaam" >
                            </li>
                            <li>
                                <input type="text" id="mail-email" name="email" placeholder="E-mail *" class="field-long" maxlength="40" >
                            </li>
                            <li>
                                <input type ="text" id="mail-phone" name="phone" placeholder="Telefoonnummer" class="field-long" maxlength = "15">
                            </li>
                            <button class="mail-submit" id="mail-submit" type="submit" name="submit">Versturen</button>
                            <span style="color: #0184b2; text-align: center; font-size: 20px; margin: 0 auto; display: block; padding-top: 10px;" class="form-message"></span>
                        </ul>
                    </form>

$("form").on("submit",function(event){
                event.preventDefault();
                var name = $("#mail-name").val();
                var lastname = $("#mail-lastname").val();
                var email = $("#mail-email").val();
                var phone = $("#mail-phone").val();
                var subject = $("#mail-subject").val();
                var information = $("#mail-information").val();
                $.post("donation-contact.php",
                    {
                    name: name,
                    lastname: lastname,
                    email: email,
                    phone: phone,
                    submit: "yes"
                    },
                    function(data){
                        $(".form-message").html( data );
                    }
                );
                });

<?php

if (isset($_POST['submit'])) {


    $email_to = "#";

    $email_subject = "#";

    $name = $_POST['name'];
    $lastname = $_POST['lastname'];
    $email = $_POST['email'];
    $phone = $_POST['phone'];


    $errorEmpty = false;
    $errorEmail = false;

    if (empty($name)) {
      echo "<span class='form-error'>Voer de verplichte velden in!</span>";
      $errorEmpty = true;
    }
    elseif (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
      echo "<span class='form-error'>Geef een geldig E-mail!</span>";
      $errorEmail = true;
    }
    else {
      $formcontent=" Naam: $name nn Achternaam: $lastname nn Email: $email nn Telefoon: $phone";
      $mailheader = "From: ".$_POST["email"]."rn";
      $headers = "From: ". htmlspecialchars($_POST['name']) ." <" . $_POST['email'] . ">rn";
      $headers .= "Reply-To: " . $_POST['email'] . "rn";
      $headers .= "MIME-Version: 1.0rn";
      $headers .= "Content-Type: text/html; charset=ISO-8859-1rn";
      mail($email_to, $email_subject, $formcontent, $mailheader);
      echo "<span class='form-success'>De mail is verzonden!</span>";
    }

  }


?>