CoreCommerce

If you choose to display an "out of stock" message on the storefront when a product is depleted, you have the option of allowing customers to request a "back in stock" reminder. This setting can be found under Settings > Inventory Settings > Inventory Tracking.

On the storefront, there will be a link that says "In Stock Notification" in the details of the out-of-stock product. When a customer clicks on this, a pop-up will appear and they will be asked for their email address. Once you put the product back in stock, an email will be sent out notifying your customers. This email is not sent out immediately—there is a script that runs each morning that checks the system to see if products have been put back in stock.

You can edit the email that is sent to your customers (called the Product Back in Stock Email) under Design > Edit Emails.

Note: This notification is not specific to variants, so the customer will just receive a general notification that the product is back in stock.

Below is a video that shows how to use this feature.