We analyzed a billion email API requests—here's what we learned

At Knock, we get asked "which email provider should I use?" all the time. Until now, comparing email provider performance has been harder than it should be. The existing resources are mostly vibes—"Best of" articles, anonymous Reddit threads, or LLM recommendations trained on that same content. Objective performance data is always missing. We believe evaluating a vendor should look the same as profiling a production system: data collected at scale, aggregated over time, under real-world conditions. So we turned to our own data. Every year, Knock sends billions of API requests to downstream email providers. With this data, we built email API benchmarks , a real-time dashboard that aggregates performance metrics across 10 major email providers. Here's what we learned. API response time: speed matters for transactional email Most email APIs had a median response time of less than 500ms, which is fast enough for most use cases. But the variance between providers tells a more interesting st