An auto-responder email is a an email which is sent from your email address as the reply to each e-mail that you get. The message is predefined and is sent automatically, so each person that contacts you via e-mail will receive it as soon as their e-mail is received on the host that manages your email messages. This function is used when you have to inform individuals about different things, such as being out of the office for a given period or that an purchase has been received and is being processed. The auto-responder email furthermore serves as a confirmation for people who make contact with you their e-mail has been received, even if you are unable to read it and get back to them right away. It could include any kind of text of your choosing and it can be modified depending on the exact occasion.