Back-in-stock alerts

When a variant is out of stock, the product page automatically offers “Notify me when available.”

• Buyers subscribe with their email; subscriptions are per-variant.
• When you restock, notifications go out automatically — with live inventory re-checked at send time so you never invite buyers to an already-sold-out product.
• Every email includes a one-click unsubscribe; rate limits prevent duplicate sends.

No setup is required — it’s on by default for all physical products with inventory tracking.