If you're using Campaign Monitor for newsletters or e-mail campaigns, you can integrate Formstack forms with your account. For example, say you have an order form and want to add a checkbox that gives a user the option to sign up for your newsletter. If the user checks that box, you can pass their info on to Campaign Monitor through your Formstack form to add them to your list.
Formstack will check to see if a user is already on your list by checking the e-mail address on the form submission. If they are, that user will be updated with the new info. If they aren't on your list, a new user will be added to your Campaign Monitor account.
To set up Campaign Monitor integration, go to the Settings page of your form, click on Settings > Integrations Hub > Email Marketing and then click on the "Add" button next to Campaign Monitor. This will add the integration to your form and take you to the integration settings.
To connect your Campaign Monitor account to your Formstack form you'll need to enter an API Key.
To find your Campaign Monitor API Key, log into your Campaign Monitor account and click on Account Settings. The API Key will be at the bottom of your settings page.
Next, you'll be shown a drop-down box of your Subscriber Lists. Choose the one you want to have Formstack populate and then choose the fields on your form that correspond to the fields on your list.