The first autoresponders were created within mail transfer agents that found they could not deliver an e-mail to a given address.
An autoresponder allows you to send email messages automatically to people who have elected to receive them (your subscribers).
[2] For example, if you've created a free report, a template, a guide, or other helpful piece of content, you can let your website visitors access it in exchange for their email address.
Popular email clients such as Microsoft Outlook and Gmail contain features to allow users to create autoresponses.
These are used by marketers to deliver a queued sequence of messages to mailing list subscribers.