diff --git a/src/MailChimp.php b/src/MailChimp.php
index e810836..4bff3f9 100644
--- a/src/MailChimp.php
+++ b/src/MailChimp.php
@@ -15,6 +15,8 @@ class MailChimp
     private $api_key;
     private $api_endpoint = 'https://<dc>.api.mailchimp.com/3.0';
 
+    private $source_ip;
+
     const TIMEOUT = 10;
 
     /*  SSL Verification
@@ -36,7 +38,7 @@ class MailChimp
      *
      * @throws \Exception
      */
-    public function __construct($api_key, $api_endpoint = null)
+    public function __construct($api_key, $api_endpoint = null, $source_ip = null)
     {
         if (!function_exists('curl_init') || !function_exists('curl_setopt')) {
             throw new \Exception("cURL support is required, but can't be found.");
@@ -44,6 +46,8 @@ public function __construct($api_key, $api_endpoint = null)
 
         $this->api_key = $api_key;
 
+        $this->source_ip = $source_ip;
+
         if ($api_endpoint === null) {
             if (strpos($this->api_key, '-') === false) {
                 throw new \Exception("Invalid MailChimp API key supplied.");
@@ -218,8 +222,8 @@ private function makeRequest($http_verb, $method, $args = array(), $timeout = se
         $response = $this->prepareStateForRequest($http_verb, $method, $url, $timeout);
 
         $httpHeader = array(
-            'Accept: application/vnd.api+json',
-            'Content-Type: application/vnd.api+json',
+            'Accept: application/json',
+            'Content-Type: application/json',
             'Authorization: apikey ' . $this->api_key
         );
 
@@ -232,6 +236,9 @@ private function makeRequest($http_verb, $method, $args = array(), $timeout = se
         }
 
         $ch = curl_init();
+        if($this->source_ip && is_string($this->source_ip)) {
+            curl_setopt($ch, CURLOPT_INTERFACE, $this->source_ip);
+        }
         curl_setopt($ch, CURLOPT_URL, $url);
         curl_setopt($ch, CURLOPT_HTTPHEADER, $httpHeader);
         curl_setopt($ch, CURLOPT_USERAGENT, 'DrewM/MailChimp-API/3.0 (github.com/drewm/mailchimp-api)');