The overwhelming consensus from both email marketing experts and official documentation is that purchasing email lists is detrimental to email marketing efforts. Purchased lists often contain outdated or inaccurate information, leading to low engagement, high bounce rates, and spam complaints. Using these lists violates anti-spam laws such as CAN-SPAM and GDPR, which can result in hefty fines and damage to sender reputation. Experts emphasize the importance of building email lists organically through permission-based methods, such as opt-in forms and lead magnets. Monitoring sender reputation using tools like Google Postmaster Tools and Microsoft SNDS is also crucial for maintaining deliverability. Guarantees from list vendors should be viewed skeptically, as they cannot control recipient behavior or list quality.