By default, all Yotpo customers are opted-in/subscribed and unsubscribers are customers who unsubscribed themselves from one or more Yotpo emails.

Once unsubscribed, a customer stops receiving Yotpo emails of any type.
A customer who organically unsubscribed themselves cannot be re-subscribed by the store owner.

However, a customer that was initially unsubscribed by the store owner via API, can be re-subscribed by the store owner using the Re-Add Email Addresses to Email Distribution Lists endpoint.

Unsubscribers endpoints

Section	Call
Remove a set of email addresses from email distribution lists	POST /apps/{app_key}/unsubscribers/mass_create
Re-add email addresses to email distribution lists	DELETE /apps/{app_key/unsubscribers/mass_delete
Retrieve a list of unsubscribers	GET /apps/:app_key/unsubscribers?utoken=:utoken