What does Autoresponder mean?
An autoresponder is a program that automatically responds to incoming email messages. An autoresponder is generally included as a feature in an email program or service, but third-party autoresponder software is available as well.
Techopedia explains Autoresponder
Autoresponders were initially designed to reply to all incoming emails when the recipient was not available to reply, such as when on vacation. The simplest autoresponder can be configured with most email programs and services, which allow a recipient to send a pre-written message to all or select incoming email messages.
An autoresponder is also used in email-based subscription processes where it is used to automatically generate and send an email on new signups. It is also used with online programs and services for broadcasting a message on specific triggers — such as notifying subscribers on their email storage quota.