Laravel Mailjet - email marked as sent but not being delivered

Question

I have just added Mailjet to my Laravel project and am sending mail using the following:

$mj = Mailjet::getClient();
$body = [
    'FromEmail' => "[email protected]",
    'FromName' => "Sender",
    'Subject' => "Contact Request",
    'Text-part' => "May the delivery force be with you!",
    'Html-part' => "<h3>May the delivery force be with you!</h3>",
    'Recipients' => [
        [
            'Email' => "[email protected]"
        ]
    ]
];
$response =  $mj->post(Resources::$Email, ['body' => $body]);

I have the following env configuration:

MAIL_DRIVER=mailjet
MAIL_HOST=in-v3.mailjet.com
MAIL_PORT=587
MAIL_USERNAME=my_mailjet_api_key
MAIL_PASSWORD=my_mailjet_secret_key
MAIL_ENCRYPTION=tls
[email protected]
MAIL_FROM_NAME="${APP_NAME}"

MAILJET_APIKEY=my_mailjet_api_key
MAILJET_APISECRET=my_mailjet_secret_key

I get a 'sent' response from the server:

array (size=1)
  'Sent' => 
    array (size=1)
      0 => 
        array (size=3)
          'Email' => string '[email protected]' (length=26)
          'MessageID' => int MessageID
          'MessageUUID' => string 'MessageUUID' (length=36)

However, nothing is being delivered to my inbox or my spam folder. The project is using Laravel 5.5.

I should also note that previous to adding Mailjet to the project I was using the Laravel Mail::send function, which stopped authenticating my email address about a month ago for some unknown reason. I'm not sure if the problem here might be related to that. You can see my previous question related to that problem here.