Webhooks 101: Reacting to Deliveries, Bounces, and Opens in Real Time

When you send an email, your job isn't finished — you've handed a message to the mail system and now you want to know what becomes of it. Did it get delivered? Bounce? Get opened? Get marked as spam? Webhooks are how your application finds out, automatically and in near real time.

What a webhook is#

A webhook is a reverse API call. Instead of your app repeatedly asking "what happened to that message?", the mail system calls you: whenever an event occurs, it sends an HTTP request to a URL you've provided, carrying the details of what just happened. Your endpoint receives it and does whatever you need — update a record, trigger a workflow, alert a human.

The mental model flip is the whole point. Polling is you knocking on the door every minute asking if anything changed. A webhook is the door telling you the moment it does.

The events worth reacting to#

The most useful events for transactional senders are:

• Delivered — the receiving server accepted the message. Useful for confirming critical mail actually arrived.
• Bounced — the message failed. This is the one to wire up first: a hard bounce should update the user's record and, ideally, feed suppression so you stop sending to a dead address.
• Complained — the recipient marked it as spam. Treat this as a strong signal to stop mailing that person and investigate what you sent.
• Opened and clicked — engagement signals, available when tracking is enabled on the hive.

Why they matter#

Webhooks turn email from fire-and-forget into a closed loop. A bounce webhook can automatically flag an invalid address the instant it happens, instead of you discovering the problem days later. A complaint webhook can pause a user's notifications before the damage spreads. Delivery confirmation can update the status a customer sees. Without webhooks, all of this is manual, delayed, or invisible.

Setting one up in Buzzmark#

Each hive can point to its own inbound webhook URL, which means you can route events per stream — your transactional hive's bounces going to one handler, another hive's to a different one. You configure the URL on the hive, stand up an endpoint that accepts the incoming requests, and start reacting to events as they arrive.

A couple of practical tips: acknowledge the webhook quickly with a success response and do heavy processing asynchronously, so a slow database write doesn't cause the sender to think your endpoint is down. And make your handler idempotent — occasionally an event may be delivered more than once, and you don't want to suppress an address or fire a workflow twice because of it.

Wire up bounces and complaints first; those two alone will do more for your list health and reputation than any amount of manual checking.