Word
Transactional email
Transactional email is mail your software sends to one person because of something that happened, using an account built for software rather than a person.
Also called: sending service, email sending service
An order confirmed, a sold-out item back in stock. It's not marketing, and it's not you typing.
Sending it needs its own account with a service built for the job. Your ordinary mailbox isn't that, software trying to send through one gets refused, or quietly filed as junk by everybody who receives it.
You only meet this if you build something that emails on its own. Almost nothing here does: the app the kit gives you doesn't send mail, deliberately, until you decide it should.