If you use Mailchimp SpeakOut! can automatically add signers to your audience (your list) if they check the “Add to mailing list” option, assuming you have it enabled and have Mailchimp enabled in the petition settings.
To enable Mailchimp go to dashboard > SpeakOut! > petitions > edit the petition > 3rd Party Extras tab. Checking the box will expose 3 fields that you need to find and enter. This is a Pro feature.
Server ID - can be found at the end of the API key e.g. if your API Key is 49bb05729a55e6a1df41c49bb683-us6, then your server ID is us6
The Audience/List ID is easy to find: https://mailchimp.com/help/find-audience-id
If you have the 2FA setting enabled, your new audience member (their terminology) will receive an email to confirm their address.
There are 2 likely scenarios that you may have. A single campaign with a number of petitions or a number of separate campaigns, each with its own petition.
In scenario 1, a single campaign, use the same Mailchimp API details for each petition.
If you have separate campaigns, assuming they are all in the same Mailchimp account, the only thing to change is the list ID for each petition. The API Key and server ID will be the same.
NOTE: for this to work, you must enable the ‘Display opt-in checkbox’ under the Display Options tab on the edit petition page. i.e. you can’t add people to your mailing list without their permission.