When people sign a petition, they have the option of opting into receiving email communication from you. By default, the box is checked next to the statement "Send me email updates." This means that if a petition signer does nothing unique, his email address will be captured and marked as emailable. 

If a petition signer un-checks the box next to the "Send me email updates" statement, the person will be marked not to receive email from you. This is based on a request from your petition signer and should not be changed.