In newsletter marketing, conversion rate most often refers to landing page signup rate: (Signups ÷ Unique Visitors) × 100. Benchmarks: 5–15% for cold traffic, 20–40% for warm traffic from your content. Conversion rate optimization (CRO) for newsletters focuses on headline clarity, lead magnet relevance, form friction (fewer fields = higher conversion), and social proof. A/B testing subject lines and landing page headlines compounds improvements over time.