You can easily enter your email address for a product that is no longer in stock. It can even be specified per size if only your size is out of stock. This is a very simple process.
Step 1:
Go to the product (and size) that is sold out.
Step 2:
Click on "keep me informed". If the button is not there, wait a while, it sometimes takes time to load.
Step 3:
Enter your email address in the pop-up and you will automatically receive an email as soon as this product is back in stock.