An auto-responder email is an e-mail that's sent back immediately to everyone who sends an e-mail to a mailbox with this feature enabled. The senders will receive the automatic answer once their e-mails are received and you will not need to do anything by hand. A couple of instances of taking advantage of auto-responder e-mails are sending an affirmation that a transaction is received and also the order will be processed or that a person is on holiday and will not be available for a particular period of time. In the first situation the option will be enabled permanently, whilst in the second one it's short-term. Even though you make use of e-mail limited to personal communication, you may use an auto-responder to let the original sender know that the e-mail has been received successfully.