Here are some steps to effectively perform keyboard navigation testing:
Open the email in a desktop email client or web-based email service. Use the Tab key to navigate through the email. Each press of the Tab key should move the focus to the next interactive element, like links and buttons. Use Shift+Tab to move backward through the elements. Ensure that all interactive elements are focusable and visually distinct when focused. Test screen reader compatibility to ensure that the content is read in a logical order.