A transactional email provides information about a specific event, such as an order, a change to an account, or a requested password reset. The event determines what the message says and when it is sent.
How does it differ from a newsletter?
A newsletter typically goes to a mailing list at a scheduled time. A transactional email goes to the person whose action or transaction triggered it. An automated promotional series is still a campaign. The purpose of the message makes the difference.
Example from an online shop
After buying something, a customer receives an email with an order number and summary. The weekly offer sent to newsletter subscribers is a separate mailing. A clear sender name and subject line help readers tell the messages apart in their inbox.
