The activated subscriber status ensures that the customer—if they are not yet stored as a newsletter subscriber in the list—is entered into the connected list with the status “Subscribed.”

If the customer's email address already exists in the list as a newsletter subscriber and has the status “Unsubscribed” and is then added as a customer with the subscriber status activated, in some cases the subscriber may be set from ‘Unsubscribed’ to “Subscribed.”

This is a bug in Mailchimp that occurs when the subscriber has been unsubscribed by the admin. If the user has unsubscribed themselves, this does not happen. Mailchimp writes:

At this time, this is still expected behavior of the API. The API is able to revert/overwrite any subscriber's status that was marked Cleaned/Unsubscribed by an admin action specifically. However, if a subscriber action (campaign or form unsubscribe, for example) puts them in a Cleaned/Unsubscribed state, then the API would not be able to overwrite or change this status.

When you activate the synchronization of unsubscribers in our plugin, the unsubscribers are temporarily stored before synchronization so that a subscriber who is “unsubscribed” does not become a subscriber with the status ‘subscribed’ under any circumstances. Synchronization can be problematic if there are a large number of subscribers who are “unsubscribed.”