Sending group messages using send grid, gives 500 Internal Server Error

Question

I want to send group messages using send grid. My group have 100 members.When I send a group message, 50 to 80 messages are delivered and then it shows a blank page as:

NetworkError: 500 Internal Server Error

My Code is,

set_time_limit (0);
$usernames = 'username'; // Must be changed to your username
$passwords = 'password';  // Must be changed to your password
// Create new swift connection and authenticate
$transport = Swift_SmtpTransport::newInstance('smtp.sendgrid.net', 25);
$transport ->setUsername($usernames);
$transport ->setPassword($passwords);
$swift = Swift_Mailer::newInstance($transport);
// Create a message (subject)
$message = new Swift_Message($subject);
// add SMTPAPI header to the message
$headers = $message->getHeaders();
$headers->addTextHeader('X-SMTPAPI', $hdr->asJSON());
// attach the body of the email
$message->setFrom($from);
$message->setBody($html, 'text/html');
$message->setTo($to);
$message->addPart($text, 'text/plain');
if ($recipients = $swift->send($message,$failures)){
    $message= 'Message sent';
}else{
    $message= "Something went wrong -  message not sent, please try later";
}

asJSON:

{
  "to": [
    ""
  ],
  "sub": {
    "-name-": [
      "anu"
    ],
    "-time-": [
      "12 PM"
    ]
  },
  "category": "initial",
  "filters": {
    "footer": {
      "settings": {
        "enable": 1,
        "text\/plain": "Thank you "
      }
    }
  }
}

Answer 1

I suggest you look into queeing solution . Check slm/queue in github for that. For long lists it may cause the server to exceed the maximum execution time, Using queue services will solve that, and all messages will be delivered in sequence.