Re-engaging an old, unmanaged email list requires a multi-faceted approach focusing on list hygiene, gradual re-introduction, personalized and incentivized content, and readily available opt-out options. Experts and marketers advise against purchasing lists or renting domains, and caution against emailing lists older than a year without thorough cleaning. Segmentation is key, allowing for tailored messaging based on past activity and demographics. Incentives, such as exclusive discounts or free resources, can encourage re-engagement. A 'last chance' email can help identify truly inactive subscribers while cleaning the list. Email verification services are crucial to remove invalid addresses, protecting sender reputation. Re-engagement should be approached slowly, sending re-opt-in messages in small batches to monitor performance. Furthermore, including an unsubscribe header and implementing a sunset policy will help in improve deliverability. In the end, getting explicit permission before sending email can improve deliverability as well as keep you out of trouble.