Building a newsletter that readers actually open

Our trade publication relied on social media for traffic, but reach has declined steadily. We relaunched a weekly newsletter with a short editor's note, three curated stories and one original analysis.

Open rates improved after we cleaned the subscriber list and sent from a named editor rather than a generic address. Now we want to grow subscribers without buying lists or using aggressive pop-ups. What tactics have worked for you to grow an engaged newsletter audience in a niche industry?