"Out of Stock" Feature
To enable this feature, begin by navigating to:
2. Online store > themes > customise
3. Navigate to "product pages"
4. Under "stock", select "out of stock email".
Another option would be to follow this guide:
All themes (both paid and free) actually don't have the ability to send emails to customers - this is controlled by the broader Shopify platform and any third-party integration you may have enabled like Klaviyo.
Once your customers enter their email addresses, this is then passed over to the "customers" list in the Shopify admin area.
We would love to make this more feature-rich, however, we are constrained by what the overall platform allows themes to implement.
The theme also sends you an email with the product name and variant.
Additional functionality would indeed require an app.
If you do decide to go ahead with an app installation, we would recommend you disable the out of stock option in the theme settings.
This app moves Products to the bottom of a Collection as opposed to hiding them:
Please see our guides on product pages.