This kind of mail is usually sent by the user his/herself. A confirm, reset password or purchase recipes are samples for transactional mails. Those mails are only sent when the user makes an action that executes that the mail is sent.
https://user-xperience.com/uxd-cont...
These mails are sent to users automatically after specific events.
Those are mails to make users aware of specific offers for a limited time.
Even if it might sound unnecessary today but e-Mail marketing still has an important impact on your ...