Adding 'gifted' email subscribers without harming deliverability requires a comprehensive strategy. Experts strongly advise prioritizing explicit permission and caution against automatic inclusion, as purchased or appended lists often underperform and damage sender reputation. Before adding subscribers, validate the list using services like Kickbox or ZeroBounce to remove invalid addresses. A gradual introduction is recommended: segment the new list, 'warm it up' with valuable content, and implement a double opt-in process. Continuous monitoring of deliverability metrics (bounce rate, spam complaints) is crucial, with swift action taken upon detecting negative trends. Authentication using SPF, DKIM, and DMARC is essential, and notifying the email marketing platform about the list addition can prevent issues. Understanding the audience through segmentation, designing engaging content, and A/B testing further optimize engagement and deliverability.