The document discusses key concepts for email marketing success, including: - Engagement is key and is expressed by customers choosing to be on a brand's email list. Having an email address is now equivalent to digital participation. - Open and click rates alone don't capture the full picture of an email's impact. Nudge effects and influence on non-openers are important. - Long-term messaging strategies for subject lines are more effective than one-off messages. Consistent frequency also drives greater engagement over time. - Email should be the primary way for brands to reach customers online since it directly and indirectly drives sales in other channels. Database size, frequency, creative, and segmentation are important for email marketing success