Subscribed (mark in imports as a 1) - these are users who have agreed to receive marketing messages.

Unknown (mark in import as blank/no value) - these are users who have entered an email address (e.g. by creating an account or making a purchase), but did not agree to receive marketing messages. You can send transactional messages from automation scenarios to customers with this status.

Unsubscribed (mark in imports as a 0) - to customers with this status we cannot and will not send any messages, because they have unsubscribed from the mailing. This change is reversible - the customer can subscribe to the newsletter again.
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