With WP Client Reports Pro, you can add a new section to the report that displays information about the audience that your client is working to build. Websites often feature mailing list sign up forms, and clients often like to know how effective those are with this helpful integration.
Mailchimp is the largest Email Campaign sending software out there thanks in part to its free ability to start collecting addresses and build out a list. You only need to start paying when you are ready to start sending out emails to a large audience.
WP Client Reports Pro only reports on one audience/list in your Mailchimp account so choose one that is most relevant to the website and the sign ups that are happening there.
Learn how to get your API key within Mailchimp to integrate WP Client Reports.