Autoresponders generate email responses to actions and events.
An autoresponder is a computer program that generates a response to an email, request, or action. Autoresponders were initially used to notify a sender of an undeliverable email, but now they are often used in email marketing. Autoresponders can give you the ability to send a customer a pre-written email when a specified event takes place, such as a customer creating an account or purchasing a product.
You can set up an autoresponder with SendGrid, by utilizing the Inbound Parse Webhook and the v3 Mail Send endpoint.
More information about autoresponders can be found here.