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 content is predefined and it is sent automatically, so each individual that contacts you via e-mail will receive it as soon as their e-mail is received on the system that takes care of your emails. This feature is used if you need to notify people about various things, such as being out of the office for a specified time period or that an order has been received and is being prepared. The auto-responder e-mail also serves as a verification for the people who get in touch with you their message is received, even if you're not able to read it and make contact with them at once. It could contain any kind of text of your preference and it may be modified depending on the exact occasion.