Microsoft's Accessibility Checker can check your email drafts for specific accessibility issues that may cause a problem to some users, and it will suggest ways to fix the barriers.
1. When composing an email go to the "Options" ribbon.
2. Then press "Check Accessibility."
3. Press "Check for accessibility issues." The results will appear in a pane to the right of your draft. If issues are found, press "Fix this" for more information, and to access the settings, you need to fix them.