Typical bitrix custom_mail function phpMailer and smtp (supports attaches)

init.php

function custom_mail ($to, $subject, $message, $additional_headers, $additional_parameters)
{
	/*\AddMessage2Log(
		'To: '.$to.PHP_EOL.
		'Subject: '.$subject.PHP_EOL.
		'Message: '.$message.PHP_EOL.
		'Headers: '.$additional_headers.PHP_EOL.
		'Params: '.$additional_parameters.PHP_EOL
	);*/

	require_once $_SERVER['DOCUMENT_ROOT'].'/vendor/autoload.php';
	$to = str_replace(' ','',$to);
	$mail = new PHPMailer;
	$mail->CharSet = 'UTF-8';
	$address = explode(',', $to);
	foreach ($address as $addr)
		$mail->addAddress($addr);

	// Просматриваем заголовки на предмет аттачей
	$headers = explode("\n", $additional_headers);
	// Определить аттачи легко - передается сепаратор таким вот образом
	$attachHeader = 'Content-Type: multipart/mixed; boundary=';
	foreach( $headers as $h )
	{
		// Если есть заголовок с ограничиителем
		if( stripos($h, $attachHeader) === 0 )
		{
			// Вытаскиваем значение сепаратора
			$bndr = substr($h, strlen($attachHeader));
			$bndr = trim($bndr, '"');
			// И дублируем его же, но в свойство phpMailer.
			$mail->ContentType = 'multipart/mixed; boundary="' . $bndr . '"';
			// I know its dirty hack
			break;
		}
	}


	if (substr_count($message, "Content-Type: text/html"))
	{

		// $mail->Encoding = '8bit';
	}
	else
	{
		// $mail->Encoding = '8bit';
		//$mail->isHTML(true); // Set email format to HTML
	}

	$mail->Subject = $subject;
	$mail->Body = $message;

	if( defined('PROJECT_SMTP_HOST') )
	{
		$mail->IsSMTP();
		$mail->SMTPDebug = defined('PROJECT_SMTP_DEBUG_LEVEL') ? PROJECT_SMTP_DEBUG_LEVEL : 0; // enables SMTP debug information (for testing)
		$mail->Host = PROJECT_SMTP_HOST;
		$mail->SMTPAuth = true; // enable SMTP authentication
		$mail->Username = PROJECT_SMTP_USERNAME;
		$mail->Password = PROJECT_SMTP_PASSWORD;		
		$mail->From = PROJECT_SMTP_FROM;
		$mail->FromName = PROJECT_SMTP_FROMNAME;
		$mail->SMTPSecure = PROJECT_SMTP_SECURITY; // "tls" or "ssl"
		$mail->Port = PROJECT_SMTP_PORT;
		//HACK: Dirty hack! if ssl not configured at hosting
		$mail->SMTPOptions = array(
			'ssl' => array(
				'verify_peer' => false,
				'verify_peer_name' => false,
				'allow_self_signed' => true
			),
		);
	}

	if( !$mail->send() )
	{
		\AddMessage2Log('Mailer Error: ' . $mail->ErrorInfo);
		return false;
	}

	return true;

}