A webhook is an automatic message that one system sends to another when something happens. Instead of your software repeatedly asking an email platform “anything new?”, the platform sends an HTTP POST request to a URL you provide as soon as an event occurs, with details of the event in the request body, usually as JSON.
In email marketing, webhooks keep other systems up to date in real time. When someone subscribes, your CRM can create a lead. When an email bounces, your database can flag the address. When someone unsubscribes, your app can update its own preferences. When an order is created, a fulfilment tool can react. Typical events include subscribed, unsubscribed, tag added, opened, clicked, bounced and complained.
Security and reliability matter. A well-designed webhook is signed, so your server can verify that the request really came from the platform and wasn’t forged; the receiver checks a signature, often an HMAC of the body made with a shared secret. Deliveries can fail when your server is down, so platforms retry with increasing delays and keep a log of attempts.
On the receiving side, respond quickly with a 2xx status and do heavy processing afterwards, so the sender doesn’t time out and retry. Handle duplicates gracefully, since a retry can deliver the same event twice. And don’t treat webhook data as instructions to run blindly: validate it and check the signature first.
A Pune SaaS startup subscribes to its email platform’s contact.unsubscribed and email.bounced webhooks. When either arrives at its server, it verifies the signature and updates the user’s notification settings in its own database within seconds.
MailNesto sends signed webhooks for events such as contact.subscribed, email.clicked, email.bounced and order.created, retries failed deliveries with increasing delays and logs every attempt.