Autoresponder is a software program that automatically responds to a certain trigger event with a pre-set message or action.
Autoresponders are mostly used for email communication. One of the most popular examples of this is the automated “out of office” messages sent in response to incoming emails.
In marketing and sales, email autoresponders can be used to deliver specific messages based on certain trigger events, e.g., newsletter subscription or opt-out, order or payment confirmation, cart abandonment, etc.
A marketing email sent in response to a certain action is called a triggered message.