An auto-responder e-mail is an email that's sent back instantly to everybody who sends a message to an email address with this feature activated. The senders will receive the automatic answer as soon as their emails are received and you'll not need to do anything manually. A couple of examples of using auto-responder messages are mailing a confirmation that a transaction has been received and the order is now being prepared or that a person is on holiday and will not be available for a specific period. In the first situation the feature can be enabled permanently, whilst in the second one it's short-term. Even though you use an email address only for private communication, you can use an auto-responder to let the e-mail sender know their e-mail is received successfully.