Several criteria can help you decide which emails to delete:
1. Inactivity: If a subscriber hasn't opened or clicked any emails in the past 6-12 months, they might no longer be interested. 2. Hard Bounces: Emails that return a hard bounce should be removed immediately. 3. Spam Complaints: Subscribers who have marked your emails as spam should be removed to protect your sender reputation. 4. Unsubscribes: Always remove users who have opted out.