Use this question as an opportunity to highlight your foundational knowledge of email marketing. Focus on clearly defining each type of email and give an example of each. If you aren't familiar with the differences between commercial and transactional emails, research these topics before the interview.

"A commercial email contains primarily promotional content aimed at getting the receiver to make a purchase or download something. They are sent out in large batches to large audiences. A transactional email is different because it's usually triggered by an action on the user's end and contains information that's unique to the individual recipient."