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When switching to Sendy, I split initial (rather old) list (all fine - created via double opt-in, used only as announced on subscription page).
After sending newsletter finished on all list parts, I began combining the list together. However, when I exported a list and re-imported it into another, all problematic emails (unsubscribed, bounced) have been imported in "Subscribed" state.
Perhaps, within the scope of a brand, when importing users into list, they should be assigned worst known state from other lists, as additional option. That way, I can combine lists without explicitly searching for bounced/whatever emails and either removing them, or manually setting appropriate state.
When you export CSVs from list, you can export just the 'Active' subscribers (less 'bounced', 'unsubscribed', 'marked as spam' and 'unconfirmed') by going to the 'Active' tab, then export the CSV: