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I manually removed emails from my list via "Mass unsubscribe" option.
Also I add emails to my list via "Import via CSV file".
I have found that previously unsubscribed emails can't be added again if I import them.
How I can added them again to my list?
You can’t re-import emails that were previously 'unsubscribed’. This prevents you from sending emails to people who have opted out of your emails. If you make them ‘Active’ again, they will very likely mark your email as spam which will then lead Amazon to suspend your Amazon SES account.
If you want to make them ‘Active’ again, you need remove them from your list(s) first, then import your CSV.