MailUp contains a handy drag-&-drop form builder that allows you to easily and quickly create responsive layout subscription forms. You can either have MailUp host the forms, or copy and paste the code onto your Web site.
Once the form has been submitted, the messages page will be displayed. This page is fully customizable in your MailUp account at Settings > List settings > Landing pages
As an alternative, you can specify a different URL on your website that your customers will be redirected to in different cases (subscription completed, duplicate email address, and so on).
MailUp uses Confirmed Opt-in by default (also called double opt-in). Once the form has been filled out, an email will be sent asking the new recipient to confirm her subscription by clicking into a link. The content and the sender of this email can be customized under Settings > List settings > Notifications > Confirmation request.
Users who confirm their subscription then receive a Welcome email, which can be personalized as well under Settings > List settings > Notifications > Welcome
You can subscribe someone to more than a list at the same time, while sending just one subscription confirmation request.
Using your forms
Of course, you can adapt existing forms so that they correctly communicate with MailUp. See more technical details on how to do so.
You can also leverage the REST or SOAP APIs to accomplish the same tasks (e.g. subscribing new recipients).
What's a "campo"?
The field code uses the word "CAMPO" because MailUp's original source code was developed in Italy. "Campo" means "Field" in Italian