(Platinum version of the plugin)
MailPoet creates newsletters, includes automated emails, post notifications and autoresponders, it is a simple newsletter solution for WordPress. MailPoet Version 2 and MailPoet Version 3
DocumentationEnabling addon

Easy to activate
To activate the add-on, simply visit the plugin page through the menu option: "Settings/Calculated Fields Form", tick the checkbox: "CFF-MailPoet", and press the "Activate/Deactivate addons" button.
MailPoet Settings

MailPoet Settings
Enter the field name for the first name, the field name for the last name, the field name for the emails, and finally, select the mailing list to associate with the form, or allow the the users select the mailing lists their want to subscribe.