HTML emails, particularly marketing and transactional emails, remain a crucial communication channel for companies due to their high return on investment, often surpassing other digital marketing strategies. Marketing emails, sent to large groups, and transactional emails, triggered by specific user actions, are essential components of a business's email strategy. Developers play a key role in crafting transactional emails, which are tied directly to a company's codebase and require an understanding of HTML email basics. Setting up a secure and authenticated email sending environment is vital, involving protocols such as SPF, DKIM, and DMARC to ensure deliverability. HTML emails often use tables for layout due to limited support for modern CSS in email clients, and inline styles are recommended for maximum compatibility. Additionally, modern tools and frameworks like MJML and Foundation for Emails simplify email development, allowing for the creation of interactive and engaging content. Despite their challenges, HTML emails offer significant opportunities for companies to create impactful customer interactions and drive business success.