BCC Postmark Transport Issue

composer.json

{
 "require": {
   "swiftmailer/swiftmailer": "~5.2",
   "wildbit/swiftmailer-postmark": "^2.1"
 }
}

testbcc.php

<?php
require 'vendor/autoload.php';

$postmarkApiKey = 'YOUR KEY';
$fromArray = ['you@email.com' => 'Chris Smith'];
$emailArray = ['email1@email.com', 'email2@email.com'];

$transport = new \Postmark\Transport($postmarkApiKey);
$mailer = new \Swift_Mailer($transport);
$message = new \Swift_Message();

$message->setSubject('Test BCC Email')
    ->setFrom($fromArray)
    ->setBcc($emailArray)
    ->setBody('<h2>Hello recipient</h2>', 'text/html');

$mailer->send($message);

running PHP 7.2.7