The following fields can be found in the MailChimp Module2 backend configuration.

Show Errors - If set to Yes will show errors on the frontend. This feature is useful for troubleshooting.

MailChimp API Key - This value is required to connect to your MailChimp account through the MailChimp API. (Note: to find your MailChimp API Key login to your mailchimp account at http://mailchimp.com then from the left main menu, click on your Username, then select "Account" in the flyout menu. From the account page select "Extras", "API Keys". Your API Key will be listed in the table labeled "Your API Keys". Copy / Paste your API key into the MailChimp Module2 setup.

MailChimp List Unique ID - This value is required so that the correct MailChimp list is selected for subscription. (Note: to find your MailChimp List ID login to your mailchimp account at http://mailchimp.com then when viewing your MailChimp Lists, select the list you wish to offer user sign-up, then click "Settings" and then "List name & defaults". Your list id will be at the top of the right column below List ID. Copy / Paste your List ID into the MailChimp Module2 setup.

Module Class Suffix - This is an optional field used to customize the MailChimp Modules2's styling

Show List Name - If set to Yes will show the List Name as it appears in your MailChimp account.

Length of Input Field - This is an optional field used to customize the character length of the modules frontend input fields.  The minimum length is 10 characters.  If left blank the default 25 characters is used.

Ask Extra Fields - If set to Yes asks for the subscribers first and last names. 

Ask Extra Fields (Pro version) - If set to Yes asks for the subscribers first and last names, and also ask for any additional fields you have defined in your MailChimp account.

Ask For Interest Groups (Pro Version) -If set to Yes asks the subscriber to choose from the interest groups you setup for this MailChimp list.

Use secure connection - If set to Yes connects to MailChimp using a secure (SSL) connection.

Check Email Address Validity - If set to Yes checks sign-up emails against a pattern.  Disable if you see a validly formatted email address that fails to go through.

UPDATE 1/05/2017 (1.0.2):

• Fixes an error in PHP versions prior to 5.5

UPDATE 1/03/2017 (1.0.1):

• Better exception handling
• Fixes a dependency problem

UPDATE 12/30/2016 (1.0):

• Connects to MailChimp API 3.0
• Better merge field handling
• User-facing validation errors are displayed by default (invalid email, required field, etc.)

UPDATE 11/17/2016 (1.0RC3.3):

• Better module parameter handling
• Fixed an SSL error
• Log and optionally display errors if the webserver cannot connect to MailChimp

UPDATE 9/8/2015 (1.0RC3.2):

• Fixed issue where Joomla's ACL blocked access to parameters and prevented the Mailchimp API call when module assigned to page with no Itemid.

UPDATE 5/14/2015(1.0RC3.1):

• When detailed error messages are turned off, all MailChimp API errors are hidden
• Able to override the success and failure messages for connecting to MailChimp
• Pro Feature: Can add rich content above and below the signup form
• Error message for blank email address now translated

UPDATE 4/25/2014:

• Fixed a bug where the module would freeze at the "Sending" message on some web servers
• Czech translation by Vilém Kužel

UPDATE 9/24/2012:

• New Catalan translation and updated Spanish translation
• Better support for MailChimp fields of type "Radio" and "Dropdown"

UPDATE 8/24/2012:

• Added blank index.html files for best practices

UPDATE 8/21/2012:

• Better handling of extended characters
• Fixed a problem with excessive server logging in some recent builds
• Better Validation
• Better CSS support
• Form Submission with Enter key
• Prevented a possible collision with other extensions
• New Languages!  Spanish and Italian transaltions by Carlotta D.

UPDATE 5/25/2012:

• "Success" message now translates successfully.
• Better handling of quote characters in language files.

UPDATE 5/15/2012:

• Dutch translation by Raoul Alderse Baas!
• The additional fields provided by MailChimp, 'First Name' and 'Last Name,' are now translated.
  (as always, any translation errors are our own, and corrections are welcome!)

UPDATE 5/9/2012:

• Fixed an error in email validation
• Email validation is now optional
• Translations!
  • Martin Erdmann - German translation
  • Martin Joset - French translation

UPDATE 11/9/2011: Major release here:

• uses the new MailChimp 1.3 API
• Fixed a problem retrieving the API key in some installs.
• general cleanup
• supports hidden fields
• install and run both in Joomla 1.5 and 1.7

UPDATE: 9/15/2009: major release here. It does several things better than before:

• uses latest MailChimp API, version 1.2.3
• corrects support for module suffix for styling
• corrects the 'merge_vars' errors
• clears fields after submit