How do testing tools detect accessibility issues?

Accessibility testing checks: alt text on images, color contrast ratios, reading order logic, link descriptiveness, and semantic HTML structure. These elements determine whether emails are accessible to people using screen readers or with visual impairments.

Automated detection: tools scan HTML for missing alt attributes, analyze color combinations against WCAG standards, flag link text that isn't descriptive, and identify structural issues affecting assistive technology navigation.

Limitations: automated testing catches technical issues but can't evaluate whether alt text is meaningful or whether content makes sense when read aloud. Use automated accessibility testing as starting point, supplemented by manual review and actual screen reader testing.