You will need to explicitly ask the user to give you their email (you can not access the email that they used to sign up to GuidedTrack). Here is detailed guide on how to Use *service to access your Mailchimp mailing list. If you have a Mailchimp account, you can access it from your GuidedTrack program. This means that you can collect the email address of your program users and add it to your Mailchimp audience, check the information of existing subscribers and update it.