TYPO3 Core

/** @var \TYPO3\CMS\Fluid\View\StandaloneView $emailView */
$email = $this->objectManager->get('TYPO3\\CMS\\Fluid\\View\\StandaloneView');
$extbaseFrameworkConfiguration = $this->configurationManager->getConfiguration(\TYPO3\CMS\Extbase\Configuration\ConfigurationManagerInterface::CONFIGURATION_TYPE_FRAMEWORK);
$email->setTemplatePathAndFilename('typo3conf/ext/xxx/Resources/Private/Templates/xxx/xxx.html');
$email->assign('args', $args['newxx']);

// Attach the message with a "cid"
$cid = $email->embed(\Swift_Image::fromPath('fileadmin/templates/xx/images/xxx_xxx.jpg'));
$email->assign('cid', $cid);

$emailBody = $email->render();

/** @var $message \TYPO3\CMS\Core\Mail\MailMessage */
$message = $this->objectManager->get('TYPO3\\CMS\\Core\\Mail\\MailMessage');
$message->setTo($sender)
>setFrom($recipient)
>setSubject($subject);

// Possible attachments here
//foreach ($attachments as $attachment) {
// $message->attach($attachment);
//}

// Plain text example
$message->setBody($emailBody, 'text/plain');

// HTML Email
$message->setBody($emailBody, 'text/html');

$message->send();