Webhooks are an easy way to get push notifications. A webhook is like an inverted API endpoint; instead of making a call to our API, you define a callback URL to which we will HTTP POST information as things happen. Your callback URL can then execute code based on the POSTs. You can think of it as defining an API endpoint for your app that will receive output from SendGrid.
We currently have two Webhooks available. The Event Webhook will POST when an email event occurs, such as a bounce or an unsubscribe. The Inbound Parse Webhook receive emails and then POSTs their constituent parameters (e.g. subject, body, and attachments) to a URL that you choose.
Webhooks can be hard to debug, for this reason we provide a guide to debug webhooks.
Keep in mind that your servers need to be robust enough to handle a large number of requests from SendGrid’s webhooks, especially if you send or receive a lot of email.