<?php 
// send mail simple
  if (isset($_POST['sd'])){
    $to = 'example@gmail.com';
    $name = $_POST[ "name"];
    $message = $_POST["message"];
    $headers = 'From: '.$_POST[ "email" ].PHP_EOL;
    if(isset($_POST["robot"])){
      if(mail($to, name, $message, $headers)){
        echo('<span class="success">Your e-mail has been sent! You should receive a reply within 24 hours!</span>');            
      }else{
        echo('<span class="error" >Houston i have a problem</span>');
      }              
    }else{
      echo('<span class="error" >Are you a robot ?</span>');
    }
  }
?>
<style>
    form {
        width: 100%;
        margin: 1em auto;
        max-width: 30rem;
    }
    form p {
        display: block;
        margin: 1em auto;
    }
    form input[type="text"],
    form input[type="email"],
    form textarea {
        display: block;
        width: 100%;
        padding: 0.5em;
        border: 1px solid #DBDBDB;
        background: #EAEAEA;
    }
    form textarea {
        min-height: 8em;
        width: 100%;
    }
    form input[type="submit"] {
        display: block;
        padding: 1em 0.2em;
        background: #FFFFFF;
        border: 1px solid #000000;
        color: #000000;
        min-width: 6em;
        text-transform: uppercase;
        transition: border 0.5s ease, color 1s ease;
    }
    input[type="submit"] {}
    form input[type="submit"]:hover {
        border-color: #FC6B5D;
        color: #FC6B5D;
        transition: border 0.5s ease, color 1s ease;
    }
    .error{
        color: red;
        text-align: center;
        margin: 0 auto;
        width: 100%;
        display: block;
    }
    .success{
        color: blue;
        text-align: center;
        margin: 0 auto;
        width: 100%;
        display: block;
    }
</style>
<form method="post">
    <p>
     Name
     <input type="text" name="name" placeholder="Your subject"  required />
    </p>
    <p>
     Email
     <input type="email" name="email" placeholder="Your email" required />
    </p>
    <p>
     Menssage
     <textarea name="message" placeholder="Your message"  required ></textarea>
    </p>
    <p>
     <input type="checkbox" name="robot"> Are your a robot?
    </p>
    <p>
     <input type="submit" name="sd" value="Send" />
    </p>
</form>