Subject Line

A subject line is the first text users evaluate in their inbox to decide whether an email deserves attention. It sets expectation, communicates relevance, and strongly influences open behavior, especially for cold or low-frequency audiences. High-performing subject lines are clear, specific, and aligned with the actual message content; misleading curiosity tactics may improve opens briefly but often increase complaints and unsubscribes. Testing should compare meaningful variations in value proposition, urgency framing, and personalization rather than minor wording tweaks only. Subject lines also interact with sender name, preview text, and segment intent, so optimization should be holistic. The best subject strategies balance open-rate improvement with downstream outcomes like click quality, conversion rate, and retention impact.