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Inactive recipients in this category will be unsubscribed. These recipients have had multiple opportunities to engage with your emails, however they have declined them all. There is no incentive for you to have these recipients in your mailing list and the system will automatically unsubscribe them. Having a cleaner (albeit smaller) mailing size will improve your engagement metrics, as shown in this case study by Marketing Sherpa.
Running a re-engagement campaign
What can you do so that your recipients do not become inactive for a long period of time? You can try to re-engagement after a certain period of inactivity. This is called a re-engagement campaign.