Functionality to sign up (via e-commerce site, or in store or via call centre), against out of stock products, to receive an email notification when an items comes back into stock.

The function should not require the customer to be logged in.

It should be possible in HQ to see a list of customers/emails signed up for notifications, which site they signed up on (therefore linked to a warehouse), and for the notifications to be automatically triggered once stock is available again for the selected item/variant, (based on buffers). The notifications would need some intelligence to send X numbers of emails based on Y stock available, (based on a parameter, and set by the retailer based on known conversion rates of these emails to actual sales). Sort order should be configurable based on known customers and a customer priority or just based on sign up date.

Once the email has been sent the customer should be removed from the list (or record updated as sent). The notification should be periodic and separated by a number of days.

For example,
Item 123 has 50 customers signed up to receive notifications
20 units are received into the distribution centre
30 customers are emailed, (As parameter set to 1.5 emails per unit)
5 days later, the available stock is now 10, send out an email notification to a further 15 customers from the list.
5 days later, available stock is now 7, send out email notification to the remaining 5 customers on the list.

A further improvement; ability for HQ employee to, for specific items / categories / maybe based on life cycle status, build an email to notify customers that the item will not be coming into stock, and recommend an alternative / related product.