Technically, it's possible to setup a signup form to submit to multiple lists. But it's not something that we, at MailChimp, can easily provide code or programming assistance to pull off. Each signup form that points to multiple lists needs to be customized to specific list settings. This type of implementation is going to required a skilled programmer to set it up. If you are not a programmer or do not have access to programming resources, you can always contact a MailChimp expert for assistance: http://experts.mailchimp.com/
Before we get into how to do this, it's best to first ask yourself if it's a good idea to do this to begin with. In cases where recipients can select to be part of multiple email lists, it's more efficient to manage their subscription preferences through one list using groups. Once a group is in place, campaigns can then be sent by segmenting using the group preference. This way, you eliminate potentially creating redundant data by managing addresses across multiple lists. For more information on how segmenting works: http://kb.mailchimp.com/article/how-can-i-send-to-a-segment-of-my-list
Also, in managing data through one list, you can take advantage of the update profile link, should recipients ever need to revise their subscription preferences.
If managing data across multiple lists has to be done, you would want to do the following:
- Create your lists under your MailChimp account and write down all appropriate list IDs. You can access unique account and list IDs by viewing source on each list's signup forms. Note the 'u' and 'id' hidden fields. In creating the forms, make sure that all common fields, across each lists, follow consistent naming conventions. For example, if you call your first name field "First Name" in one list, it should be named the same thing in all lists.
- Once you have your lists in place and IDs recorded, you'll need to add a signup form to your website that reflects the fields that your lists in MailChimp are expecting you to collect. If you need it, you can always grab form code by navigating to the Lists page, clicking the list drop down, and selecting Signup forms. On the Signup forms page you can select Embedded forms to pull up the source HTML code for an embedded version of your form.
- Now comes the custom step to the process. When setting up the forms in your website you need to create a page in your website that your forms can submit to. The page created needs to be designed to gather and validate data collected and once data is finalized, submitted back to the appropriate list hosted on MailChimp using an API connection.
Rather than having content preferences in your signup form reference a content type they will instead reference the list that you want your subscriber's data sent to. For example if you set up 3 lists, List A, List B, List C, your signup form may have a field that offers, "Would you like to signup for content A, B or C?". Once sent to your website your code would then parse what is submitted and based on what's selected send the recipients info to the appropriate list.