How to use your own Mailgun subject line?
To use your own Mailgun subject line you need to configure your own Mailgun token.
1.) For that you need to open up a Mailgun account first, you can set one up here: https://signup.mailgun.com/new/signup
Once you signed-up you can access your token, here you will find a short description on how to get to your API token.
2.) Go to the "My Apps" section in Shopstory and connect Mailgun by using your token.
3.) Configure the application and set your desired subject line (see screenshot)