Solving Connectivity Issues

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.

Advanced Users: If you have SSH access to your hosting server, please skip to the bottom of this page.

First of all, we should make sure that your webhost has the PHP CURL module 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 code on my site which relies on the PHP CURL module. Can you please confirm the following things?

- PHP CURL is installed and updated to at least version 7.35
- Requests to https://* 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 there somewhere between all the other installed modules.

Details on the various error messages

MailChimp & Plugin License Settings - MailChimp for WordPress Lite ‹ Kinstantly — WordPress 2015-10-14 15-57-30

"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 of your website 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.

When this happens, we recommend you to change your 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 IP address.
  • 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.


If you have SSH access to your server, running the following command provides a quick way to test if remote requests to the MailChimp server should actually work and will otherwise give a more detailed error message.

curl -v
Replace us1 with the characters in the end or your API key, after the minus sign.
Replace test with everything in front of the minus sign of your API key.

If you find the word "Akamai" anywhere in the response your server is blocked by the Akamai firewall that MailChimp uses, see the paragraph above.

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