Opting out of a list means a subscriber has asked not to be added to your list or has asked to be removed from your list. When a subscriber leaves the list, they have "opted out", and cannot be re-added to your list. Subscribers who report your messages as spam are automatically unsubscribed, and considered to be "opted out".
Once a subscriber has opted out of your list, they cannot be re-added. Deleting your unsubscribed addresses will not remove opt-out records. This is done to prevent the accidental resubscribing of addresses which do not want to receive email from your list.
Subscribers that you unsubscribe are not considered opted out; only subscribers who remove themselves or report your list as spam are opted out.
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