Subscribe form works as an e-mail newsletter.
To activate the Campaign Monitor service, you need to replace the form’s [#code.rd-mailform] class with .campaign-mailform and copy the form's action and the name of the input field from the form generated by Campaign Monitor service.
To activate such form with an enabled MailChimp service, replace the .rd-mailform class with .mailchimp-mailform and the form's action with MailChimp subscription URL.