Send parameters from a form to a mail with php and hrml

Question

I am working on this project where the end user will be able to contact the administrator from a form, and the message will deliver into a mail box. The user fills in the contact form with the necessary details and when the send button is clicked, it sends the form to the mail in the code.

This is the contact.html page

<form id="contactform" class="" action="contact.php" name="contactform" method="post">
            <div>
              <input type="text" name="first_name" id="first_name" class="form-control"
                                        placeholder="First Name"/>
            </div>
            <div>
              <input type="text" name="last_name" id="last_name" class="form-control"
                                        placeholder="Last Name" />
            </div>
            <div>
              <input type="email" name="email" id="email" class="form-control"
                                        placeholder="Your Email" />
            </div>
            <div>
              <input type="text" name="phone" id="phone" class="form-control"
                                        placeholder="Your Phone"/>
            </div>            
            <div>
              <input class="form-control" rows="6" name="comments" id="comments" type="text" class="message-box" placeholder="Message" />
            </div>
            <div class="d-flex ">
              <button type="submit" value="SEND" id="submit">
                SEND
              </button>
            </div>
          </form>

This is the contact.php code

<?php

if(!$_POST) exit;

// Email address verification, do not edit.
function isEmail($email) {
    return(preg_match("/^[-_.[:alnum:]]+@((([[:alnum:]]|[[:alnum:]][[:alnum:]-]*[[:alnum:]])\.)+(ad|ae|aero|af|ag|ai|al|am|an|ao|aq|ar|arpa|as|at|au|aw|az|ba|bb|bd|be|bf|bg|bh|bi|biz|bj|bm|bn|bo|br|bs|bt|bv|bw|by|bz|ca|cc|cd|cf|cg|ch|ci|ck|cl|cm|cn|co|com|coop|cr|cs|cu|cv|cx|cy|cz|de|dj|dk|dm|do|dz|ec|edu|ee|eg|eh|er|es|et|eu|fi|fj|fk|fm|fo|fr|ga|gb|gd|ge|gf|gh|gi|gl|gm|gn|gov|gp|gq|gr|gs|gt|gu|gw|gy|hk|hm|hn|hr|ht|hu|id|ie|il|in|info|int|io|iq|ir|is|it|jm|jo|jp|ke|kg|kh|ki|km|kn|kp|kr|kw|ky|kz|la|lb|lc|li|lk|lr|ls|lt|lu|lv|ly|ma|mc|md|me|mg|mh|mil|mk|ml|mm|mn|mo|mp|mq|mr|ms|mt|mu|museum|mv|mw|mx|my|mz|na|name|nc|ne|net|nf|ng|ni|nl|no|np|nr|nt|nu|nz|om|org|pa|pe|pf|pg|ph|pk|pl|pm|pn|pr|pro|ps|pt|pw|py|qa|re|ro|ru|rw|sa|sb|sc|sd|se|sg|sh|si|sj|sk|sl|sm|sn|so|sr|st|su|sv|sy|sz|tc|td|tf|tg|th|tj|tk|tm|tn|to|tp|tr|tt|tv|tw|tz|ua|ug|uk|um|us|uy|uz|va|vc|ve|vg|vi|vn|vu|wf|ws|ye|yt|yu|za|zm|zw)$|(([0-9][0-9]?|[0-1][0-9][0-9]|[2][0-4][0-9]|[2][5][0-5])\.){3}([0-9][0-9]?|[0-1][0-9][0-9]|[2][0-4][0-9]|[2][5][0-5]))$/i",$email));
}

if (!defined("PHP_EOL")) define("PHP_EOL", "\r\n");

$first_name     = $_POST['first_name'];
$last_name     = $_POST['last_name'];
$email    = $_POST['email'];
$phone   = $_POST['phone'];
// $select_price   = $_POST['select_price'];
// $select_service   = $_POST['select_service'];
// $subject  = $_POST['subject'];
$comments = $_POST['comments'];
// $verify   = $_POST['verify'];

if(trim($first_name) == '') {
    echo '<div class="error_message">Attention! You must enter your name.</div>';
    exit();
}  else if(trim($email) == '') {
    echo '<div class="error_message">Attention! Please enter a valid email address.</div>';
    exit();
} else if(!isEmail($email)) {
    echo '<div class="error_message">Attention! You have enter an invalid e-mail address, try again.</div>';
    exit();
}

if(trim($comments) == '') {
    echo '<div class="error_message">Attention! Please enter your message.</div>';
    exit();
}

// if(get_magic_quotes_gpc()) {
//  $comments = stripslashes($comments);
// }


// Configuration option.
// Enter the email address that you want to emails to be sent to.
// Example $address = "joe.doe@yourdomain.com";

//$address = "example@themeforest.net";
$address = "olushalom001@resolveng.com";


// Configuration option.
// i.e. The standard subject will appear as, "You've been contacted by John Doe."

// Example, $e_subject = '$name . ' has contacted you via Your Website.';

$e_subject = 'You\'ve been contacted by ' . $first_name . '.';


// Configuration option.
// You can change this if you feel that you need to.
// Developers, you may wish to add more fields to the form, in which case you must be sure to add them here.

$e_body = "You have been contacted by $first_name." . PHP_EOL . PHP_EOL;
$e_content = "\"$comments\"" . PHP_EOL . PHP_EOL;
$e_reply = "You can contact $first_name via email, $email or via phone $phone";

$msg = wordwrap( $e_body . $e_content . $e_reply, 70 );

$headers = "From: $email" . PHP_EOL;
$headers .= "Reply-To: $email" . PHP_EOL;
$headers .= "MIME-Version: 1.0" . PHP_EOL;
$headers .= "Content-type: text/plain; charset=utf-8" . PHP_EOL;
$headers .= "Content-Transfer-Encoding: quoted-printable" . PHP_EOL;

if(mail($address, $e_subject, $msg, $headers)) {

    // Email has sent successfully, echo a success page.

    echo "<fieldset>";
    echo "<div id='success_page'>";
    echo "<h1>Email Sent Successfully.</h1>";
    echo "<p>Thank you <strong>$first_name</strong>, your message has been submitted to us.</p>";
    echo "</div>";
    echo "</fieldset>";

} else {

    echo 'ERROR!';

}

After running the code, this is the result.