Final answer:
The correct answer is option C. Edit an email's HTML to list the custom brand font in the style tag's font-family property.
Step-by-step explanation:
The recommended best practice for font usage in email is to Edit an email's HTML to list the custom brand font in the style tag's font-family property. This allows the custom brand font to be used in the email, ensuring consistency with the brand's guidelines.
Using a web-safe font that closely matches the brand's custom font (option A) may not accurately represent the brand's identity, while building an email as one image or using multiple images for text (options B and D) can create issues with accessibility, load times, and rendering across different email clients.