How can A/B testing improve deliverability (via engagement)?

A/B testing improves deliverability indirectly by optimizing the engagement signals that mailbox providers use to evaluate sender reputation.

Higher open rates from better subject lines tell providers that recipients recognize and want your mail. More clicks from improved CTAs demonstrate genuine interest beyond passive opening.

Lower unsubscribe rates from better content matching show that your audience finds value. Reduced complaints from appropriate frequency testing signal healthy sender-recipient relationships.

Each positive engagement signal feeds into reputation calculations at Gmail, Microsoft, and other providers. Better engagement leads to better inbox placement, which leads to more engagement opportunities.

Testing creates a virtuous cycle. Optimized emails generate better signals, better signals improve deliverability, and better deliverability gives more people the chance to engage.