Newsletter terms

A/B testing (or split testing) is the process of comparing two versions of a newsletter to determine which one performs best based on real subscriber data.

Click-through rate (CTR) measures the percentage of recipients who take action by clicking a link in your newsletter. It is the most reliable metric for true engagement in 2026.

Double opt-in is the gold standard for newsletter list health. Learn why confirmed subscriptions are essential for deliverability in 2026.

An Email Service Provider (ESP) is the core engine of your newsletter. Learn why the definition of an ESP is shifting toward 'Creator Operating Systems' in 2026.

Open rate is the percentage of subscribers who open your newsletter. Learn why this metric is changing and how to measure true engagement in 2026.

The preheader is the silent hero of your newsletters open rate. Learn how to optimize this "second headline" for 2026 inbox success.

The subject line is the most important sentence in your newsletter. Discover how to craft high-converting headlines using 2026 best practices and AI.

A subscriber is the lifeblood of your newsletter. Learn how the definition is shifting from "email count" to "active engagement" in 2026.