Mandrill not working for me

[look]

$args = array(

    'key' => 'cfe37894-0ccb-4a17-9cee-************',

    'message' => array(

        "html" => "<p>\r\n\tHi Adam,</p>\r\n<p>\r\n\tThanks for <a href=\"http://mandrill.com\">registering</a>.</p>\r\n<p>etc etc</p>",

        "text" => null,

        "from_email" => "a...@yyyl.com",

        "from_name" => "SIVOnline",

        "subject" => "Your recent registration",

        "to" => array(array("email" => "a...@xxx.com")),

        "track_opens" => true,

        "track_clicks" => true,

        "auto_text" => true

    )   

);

$curl = curl_init('https://mandrillapp.com/api/1.0/messages/send.json');

curl_setopt($curl, CURLOPT_POST, true);

curl_setopt($curl, CURLOPT_HEADER, false);

curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);

curl_setopt($curl, CURLOPT_HTTPHEADER, array('Content-Type: application/json'));

curl_setopt($curl, CURLOPT_POSTFIELDS, json_encode($args));

$response = curl_exec($curl);

curl_close($curl);

var_export($response);

I am using the above code to send mail via mandrill but it is giving me reply as =>     "false"