Working Version

<?php
/*
Plugin Name: Ralrom Simple Contact Form
Plugin URI: website
Description: Creates a contact form on the page using wordpress shortcode API. Inspired by wptuts.
Version: 1.0
Author: Robert Al-Romhein
Author URI: webiste
*/


function get_sender_ip() {
    if (isset($_SERVER["HTTP_X_FORWARDED_FOR"])) {
        return $_SERVER["HTTP_X_FORWARDED_FOR"];
    }
    elseif (isset($_SERVER["HTTP_CLIENT_IP"])) {
        return $_SERVER["HTTP_CLIENT_IP"];
    }
    else {
        return $_SERVER["REMOTE_ADDR"];
    }
}

function contact_form_sc(){

    //shortcode attributes
    extract(shortcode_atts(array(
        "email" => get_bloginfo('admin_email'),
        "dreamhost_email" => "[email protected]",
        "subject" => "",
        "label_name" => "Name:",
        "label_email" => "Email:",
        "label_subject" => "Subject:",
        "label_message" => "Message:",
        "label_submit" => "Send",
        "error_empty" => "Please fill in all the fields.",
        "error_noemail" => "Please enter a valid e-mail address.",
        "success" => "Thank you for your e-mail! I'll get back to you shortly."
    ), $atts));

    if ($_SERVER['REQUEST_METHOD'] == 'POST') {
        $error = false;

        foreach ($_POST as $field => $value) {
            if(!isset($field)){
                $error = true;
                $result = $error_empty;
            }
        }

        //sanitize all fields
        $s_name = sanitize_text_field($_POST["client_name"]);
        $s_subject = sanitize_text_field($_POST["subject"]);
        $s_message = esc_textarea($_POST["message"]);

        //sanitize email
        if(is_email($_POST["email"])){
            $s_email = is_email($_POST["email"]);
        } else {
            $error = true;
            $result = $error_noemail;
        }
        //send email if no error
        if(!$error){
            $email_subject = "[" . get_bloginfo('name') . "] " . $s_subject;
            $email_message = "Sender IP: " . get_sender_ip() . "\nFrom: " . $s_name . "\nReply to: " . $s_email . "\nMessage:\n\n" . $s_message;
            $headers[] = 'From: RalRom Contact Form <[email protected]>';
            $headers[] = 'Cc: Contact RalRom <[email protected]>';
            wp_mail($email, $email_subject, $email_message, $headers);
            $result = "<h1>" . $success . "</h1>";
            $sent = true;
        }
    }

    $email_form = '
    <div id="contact"><a name="contact"></a>
    <div id="intro">
    <h1>Nice to meet you</h1>
    What would you like?

    </div>
    <!--intro-->

    <form method ="post" action="' . get_permalink() . '">
    <div class="field"><label for="cf_name">'.$label_name.'</label>
    <input id="cf_name" tabindex="1" type="text" name="client_name" value="Enter your name" required/></div>
    <!--field-->
    <div class="field"><label for="cf_email">' . $label_email . '</label>
    <input id="cf_email" tabindex="2" type="email" name="email" value="Enter your e-mail address" required/></div>
    <!--field-->
    <div class="field"><label for="cf_subject">' . $label_subject . '</label>
    <input id="cf_subject" tabindex="3" type="text" name="subject" value="Enter your subject" required/></div>
    <!--field-->
    <div class="field"><label for="cf_message">' . $label_message . '</label>
    <textarea id="cf_message" tabindex="4" cols="30" name="message" rows="10" required></textarea></div>
    <!--field-->
    <input class="send" tabindex="4" type="submit" name="submit" value="' . $label_submit . '" />

    </form></div>';

    return $info.$email_form;
}

add_shortcode('contact', 'contact_form_sc');