Make sure you have checked the following:
check mybookprogress settings – go to the promote tab
make sure all the boxes are filled and if they are done properly they will make a green check mark.
Have you made a test email from here? It should give you the option then you can see if it is working.
I tested the process on our test server and when someone subscribes they should get an email in their inbox from Mailchimp that gives them the option to subscribe. Once they are subscribed it will depend on when you set up the mailchimp update to go out as to when anyone will receive updates about your book progress.