What is heading hierarchy in HTML email?

Heading hierarchy means using H1, H2, H3 tags in logical order to create content structure. Screen readers use headings for navigation-users can skip between sections. Proper hierarchy also helps sighted readers scan.

Best practices: One H1 per email-the main topic/headline. H2s for major sections-don't skip from H1 to H3. H3s and below for sub-sections-nest logically. Don't use headings just for styling-use CSS for font sizes instead. Keep hierarchy consistent-same structure across emails builds familiarity.

Headings are navigation, not decoration. When you style text as large and bold but use a <p> or <div>, screen readers don't know it's a heading. Users can't jump to it. Use actual heading tags, style them as needed. Structure and appearance can both be right.