Summary  
This chapter explains how to build and continuously optimize a message delivery system by configuring authentication protocols, enforcing progressive rate limits, validating recipient data, and running iterative A/B tests to monitor and improve delivery metrics.

General domain of usage  
Email marketing

**Email deliverability = your ability to land in the inbox, not spam**.

Three core factors control it:
1. **Domain and technical reputation**: maintain low bounce and complaint rates, remove inactive contacts regularly, and continuously test subject lines, timing, and CTAs to keep improving performance and inbox placement;
2. **List quality**: regularly verify contacts with tools like MillionVerifier, remove invalid, bounced, or inactive addresses, and ensure bounce or complaint rates stay below 2%;
3. **Email content and sending practices**: avoid spam triggers such as excessive images, all-caps text, spammy phrases like "free" or "act now", and missing unsubscribe links. Follow best practices: keep a healthy text-to-image ratio (or send text-only for maximum safety), include a clear unsubscribe option, send from a real name and address, and respond to incoming replies to boost engagement and reputation.

Which factor has the biggest long-term impact on sender reputation?

Learn how to build, launch, and optimize email campaigns that drive real results. Focus on growing a high-quality audience, crafting effective messages, automating customer journeys, and using data to continuously improve performance and deliverability.

Deliverability, Reputation and Continuous Optimization