Transactional emails are an essential part of an eCommerce website that contains information the recipient wants after completing a transaction.  Whenever your customer makes some purchase form your e-store then they receive a transactional email related to order confirmation and shipping details. These types of mail have a high open-rate because these types of emails contain order completion info, account activation email,  password reset email and many more. That’s why they are called transactional emails. Read more on https://bit.ly/2IQAtq4