Do Back in Stock sign-ups join my email marketing list? (Essent Preorder Back in Stock app)

No. When a customer signs up with the Notify me form, the app stores their email (and phone, if you collect it) only to send the back in stock alert. It doesn't create a Shopify customer and doesn't change anyone's email marketing consent in Shopify.

Ways to use sign-ups in your marketing tools

• Omnisend. Connect it under Back in Stock → General Settings → Integrations. Each sign-up is added to Omnisend as a contact, with the tag you set there. See How to integrate with Omnisend.
• Shopify Flow. The Back in stock signup created trigger starts a workflow each time someone signs up, with the customer and product details. See Shopify Flow triggers and actions.
• Export. Download the subscriber list from Products & Notifications → Export notifications. See Where can I see or export my Back in Stock subscribers?

Only add people to a marketing list if they agreed to it. Signing up for a restock alert isn't consent to marketing emails.