After you’ve integrated your form with SalesForce, MailChimp, AWeber, VerticalResponse, Top Producer or iContact, you can add an opt-in checkbox to your form. Like this, form users will be requested to tick the checkbox in order to be added to your mailing list and the bounce rate of your mailing list will drop.
1.In your Form Editor, drag a multiple choice field to the main view.
2. In its Edit panel on the left side of the screen, delete Choice 2 and Choice 3 and replace Choice 1 with the message you want form user to see (e.g.: Add me to your mailing list).
3. Remove the field label and your checkbox is ready to find some functionality.
4. Go to your Settings → Applications section. In the application box, in the dropdown list labeled Send, select Only if choice is checked: (opt-in message).
5. Press Save.