Having trouble setting up the connection between your WordPress site and the Mailchimp servers? This can be caused by a number of factors. Let’s go trough them step by step.

First of all, we should make sure that your webhost has the PHP CURL extension installed and updated to a recent version and if they are not blocking requests to the Mailchimp server.

Here’s a copy-and-paste message you can send your webhost for them to check:

I am currently installing a WordPress plugin on my site which uses the PHP CURL extension. Can you please confirm the following?

– The PHP CURL extension is installed and updated to at least version 7.35
– HTTP requests to https://api.mailchimp.com/ are not blocked

Thanks in advance!

Checking, and optionally acting on these things, should really be no more than a matter of minutes for your webhost.

If you want to check what version of cURL is installed by yourself you can install the WordPress plugin phpinfo() and search the info page for "cURL". If cURL is installed it will display the version number along with information on all the other installed PHP extensions.

Details on the various error messages

Read the error message you are seeing closely and compare it to the section below for additional hints on the error you are experiencing.

“Unable to connect”

This notice means that you have a very old version of PHP-CURL installed (over 5 years old, to be specific).

To fix it: ask your webhost to update cURL to at a more recent version, preferably version 7.35 or up.

“Connection refused” or “Connection timed out”

These are firewall issues. Most likely, your webhost is blocking access to the Mailchimp API servers.

To fix it, you should ask your webhost for the following URL to be whitelisted:


If you are a user of our premium plugin, please ask them to whitelist the following address as well. This is the server address that is used for retrieving new plugin updates:


cURL error 6: Couldn’t resolve host

This indicates a problem with the DNS setup on your hosting server. Please ask your hosting provider for help.

“SSL certificate problem”

This means that something failed in setting up the encrypted connection with the Mailchimp server. This is a known bug affecting WordPress 4.4 which will be fixed in WordPress 4.4.1.

As a temporary workaround, you can add the following piece of code to your theme its functions.php file.

add_filter('mc4wp_use_sslverify', '__return_false');

403 “Forbidden” or 503 “Service Unavailable”

This means that the IP address that your hosting provider uses for outbound cURL connections made by PHP is blacklisted by the Akamai firewall (because of poor reputation). Akamai is the firewall Mailchimp and many other major websites use to protect their servers, which is why this is somewhat harder to fix.

Note that many hosting providers use shared IP addresses, meaning that your website IP is shared with a number of their users. It’s possible that another client of your hosting provider did something to get the IP blacklisted, completely out of your control.

When this happens, we recommend you to change your hosting IP address because having a bad reputation at Akamai does not just affect the Mailchimp API.

There are various ways to go about this.

  • Ask your webhost for a new hosting IP address. Most hosting providers are able to sell you a Private hosting IP or move you to another shared hosting IP.
  • Migrate to a new webhost if your hosting company is unwilling to fulfill your request.
  • Configure your server to connect to the Mailchimp API server using a proxy.