public function beforeSendPerformed(Swift_Events_SendEvent $evt)
{
$message = $evt->getMessage();
$headers = [];
foreach ($message->getHeaders()->getAll() as $header) {
$headers[$header->getFieldName()] = $header->getFieldBody();
}
$this->timeline->startEvent('email ' . $message->getId(), 'Sending an email message', null, ['from' => $this->addressToString($message->getFrom()), 'to' => $this->addressToString($message->getTo()), 'subject' => $message->getSubject(), 'headers' => $headers]);
}