$apikey = "Su API";
$nombre_del_remitente = urlencode("Su nombre");
$sender_email = "votremail@domaine.com";
$mail_subject = urlencode("API TEST OK");
$mail_body = urlencode("¡HOLA MUNDO! EMAIL TEST");

$correo electrónico del destinatario = "mailDestination@domaine.com";

$URL = "https://api.emailroot.com/smtp/mail/send/?apikey=".$apikey."&nombre-del-remitente=".$nombre-del-remitente."&correo-del-remitente=".$correo-del-remitente."&correo-del-destinatario=".$correo-del-destinatario ."&charset=".$charset."&mail_subject=".$mail_subject."&mail_body=".$mail_body."&format=html";

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $URL);
curl_setopt($ch, CURLOPT_RETTRANSFER, 1);

echo $output = curl_exec($ch);
curl_close($ch);