How we built link tracking to be reliable, fast, and secure

We recently released a new enhancement to email sending called “Link Tracking” which provides insights into how recipients interact with emails, including preferred browsers and locations. To achieve this, we built a reliable, fast, and secure system that uses a geo-distributed approach, making it highly available even under circumstances where other parts of the Postmark infrastructure may be experiencing delays or issues. The system uses full-time HTTPS to prevent eavesdropping and relies on HMACs to validate requests. Each tracked link is completely standalone, minimizing latency and ensuring strong consistency. We've deployed Link Routers in pairs across three regions worldwide, capable of handling approximately 1,900 requests per second, with the ability to easily add capacity as usage grows.