Paid account holders with custom coding experience or access to a developer may choose to handle signup form errors on their own websites. The Form Builder's advanced mode allows users to customize code and add META redirects to handle error messages. These features are completely optional.
If you prefer to handle signup form errors on your own, instead of having MailChimp manage them, use a META redirect to pass signup form data back to your domain using this code.
<meta http-equiv="Refresh" content="0;url=http://www.domain.com/newsletter.phtml?EMAIL="*|EMAIL|*"&FNAME="*|FNAME|*"&LNAME="*|LNAME|*"">
The URL should be a full path to your newsletter subscriber page. To grab the list variables' names, navigate to the Lists page and view your merge tags.
To complete this process, you'll need to know how to process GET variables in your site and make sure your list 'id' is a part of any form you submit back to our domain.
Instead of using a META redirect, you could also use our API. You'll still most likely want to add a META redirect on the final confirmation screen to make the sign-up process feel totally seamless to your subscribers.