How does click tracking work?

So when When you click a link in a marketing email, you almost never land directly on the destination. There's a middle step. That middle step is click tracking.

Here's what happens: when you create a campaign, your ESP replaces every link with a tracking URL, something like https://click.esp.com/t?id=abc123&url=encoded_destination. When a recipient clicks, their browser hits the tracking server first. The server logs the click (time, unique identifier, sometimes device and location data), then immediately redirects to the real destination. The whole thing happens in milliseconds and recipients rarely notice.

Each tracking URL encodes a campaign identifier and a per-recipient identifier, so the ESP knows not just that a link was clicked, but who clicked it and when. That's how you get per-subscriber engagement data, not just aggregate click counts.

A few things worth knowing: the redirect domain in those tracking URLs matters for deliverability. If it's a shared domain that gets blocklisted, your links get flagged. That's why serious senders set up custom tracking domains using a subdomain they own. Also, privacy regulations like GDPR require that you disclose tracking to recipients, and some email clients (especially enterprise security gateways) rewrite links again, which can break your tracking.

If you want to verify that your tracking setup is working correctly and not causing redirect chains that hurt deliverability, you can test individual URLs by following them step by step and checking each response code. A clean setup should be a single redirect, not a chain of three or four hops.