For me, as someone who has only recently become familiar with these concepts, the line between marketing and transactional emails was really blurred. However, I found a great article about these concepts and it became very clear to me what the comparison and difference between them are. In a nutshell, a marketing email you receive from various stores or manufacturers about a particular product, item, service or discount. It's a promotional email and it doesn't imply your response. A transactional email implies that a specific user will receive it and stipulates that the customer performs a specific action after receiving the email.