Hi, looking in another plugin I found this code to send email:
$modx->getService('mail', 'mail.modPHPMailer');
$modx->mail->set(modMail::MAIL_BODY, $_msg);
$modx->mail->set(modMail::MAIL_FROM, $_from);
$modx->mail->set(modMail::MAIL_FROM_NAME, $_fromName);
$modx->mail->set(modMail::MAIL_SENDER, $_sender);
$modx->mail->set(modMail::MAIL_SUBJECT, $_subject);
$modx->mail->address('to', $email, $name);
$modx->mail->address('reply-to',$_reply);
$modx->mail->setHTML(true);
$sent = $modx->mail->send();
$modx->mail->reset();
eventually you can get "$_from" and other field from system settings