How can I automatically notify customers when products come back in stock?

You can now automatically alert interested customers when products that are set not to allow backorders come back into stock:

Once customers have registered their email addresses for the Back-In-Stock notification, when the SKUs they are interested in are back in stock, the system will use the Back-In-Stock Email Notification transactional email template under Marketing > E-Mail Templates > Transactional E-Mail Templates to automatically notify your customers that the product is now available.

Each customer who submits their email address also appears under Marketing > E-Mail Lists Manager, where you can view and Export the list for your own use through any 3rd party notification systems you want to use: