$apikey = "Sua API";
$sender_name = urlencode("Seu nome");
$sender_email = "seumail@domínio.com";
$mail_subject = urlencode("API TESTE OK");
$mail_body = urlencode("OLÁ MUNDO! TESTE DE E-MAIL");

$recipient_email = "mailDestination@domain.com";

$URL = "https://api.emailroot.com/smtp/mail/send/?apikey=".$apikey."&sender_name=".$sender_name."&sender_email=".$sender_email."&recipient_email=".$recipient_email ."&charset= ".$charset."&mail_subject=".$mail_subject."&mail_body=".$mail_body."&format=html";

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

eco 1TP4Allput = curl_exec($ch);
curl_close($ch);