Inactive Subscribers: Subscribers who haven't engaged with your emails for a long period should be removed. Keeping them can negatively impact your engagement rates and deliverability. Outdated Content: Ensure that your content is always relevant and up-to-date. Old promotions or irrelevant information should be deleted. Duplicate Entries: Duplicate email addresses can skew your analytics and waste resources. Make sure to regularly clean your list to remove duplicates. Unsubscribed Users: It's crucial to delete users who have opted out to comply with privacy regulations like GDPR and CAN-SPAM Act.