mailgun.php

<?php
$mgClient = new Mailgun('YOUR_API_KEY');
$domain = "YOUR_DOMAIN_NAME";

$result = $mgClient->sendMessage($domain, array(
    'from'    => 'Remetente <mailgun@YOUR_DOMAIN_NAME>',
    'to'      => 'Destinatario <YOU@YOUR_DOMAIN_NAME>',
    'subject' => 'Hello',
    'text'    => 'Testing some Mailgun awesomness!'
));