Email API benchmarks
Real-time performance, reliability, and uptime benchmarks for top email providers, powered by proprietary data from billions of messages sent through Knock.
Performance at a glance
Sort and filter providers by response time, error rate, delivery speed, and growth.
| Provider | Message volume | Median response time | Error rate | Growth |
|---|---|---|---|---|
 | 500M+ | 22ms | 0.00% | 2nd |
 | 25M–100M | 33ms | 0.00% | 4th |
 | 10M–25M | 79ms | 0.07% | 1st |
 | 100M–500M | 123ms | 0.00% | 5th |
 | 25M–100M | 127ms | 0.00% | 3rd |
 | 1M–10M | 128ms | 0.00% | 8th |
 | <1M | 138ms | 0.00% | 7th |
 | <1M | 265ms | 0.01% | 9th |
 | <1M | 288ms | 0.22% | 10th |
 | <1M | 409ms | 0.00% | 6th |
Compare providers
Pick any two providers for a head-to-head comparison of performance, reliability, and pricing.
| Provider | Volume | Median response time | Error rate | Growth |
|---|---|---|---|---|
| Amazon SES | 25M–100M | 127ms | 0.00% | 3rd ↑ |
| Resend | 10M–25M | 79ms | 0.07% | 1st → |
Explore provider benchmarks
Explore detailed performance benchmarks, feature comparisons, and pricing for each provider.
Our methodology
How we collect, measure, and present the data behind these benchmarks.
Time range
All metrics reflect a trailing 90-day window. Point-in-time load tests don't capture the variability of a production system handling thousands to millions of requests daily, so we use a longer window to surface the effects of system congestion and public incidents without penalizing providers that are actively improving.
Message volume
Volume represents the total number of sampled email API requests routed through Knock during the period. Because Knock is an orchestration layer, we cannot influence the sending patterns of our customers, so volume varies by provider. To normalize for this, we group providers into volume bands (e.g. <1M, 1M–10M, 10M–25M) that indicate how statistically confident we are in the observed metrics. Providers with low volume are flagged so you can weigh the results accordingly.
Response time
Response time is measured as the elapsed time from when Knock sends an API request to when the provider returns a 200 status indicating message acceptance (a "sent" event in Knock). We compute percentiles (p50, p90, p95, p99) using the quantileExact function in ClickHouse, meaning values are exact and not sampled. The measurement includes HTTP connection pooling time and network latency, applied consistently across all providers. If Knock's automatic retry logic is triggered by a retryable error, the total retry duration is included in the response time for that request.
Error rate
Error rate is the ratio of requests that received a 5xx status code (500, 502, 503, etc.) to total requests for the period. We treat all 5xx responses equally — whether a 503 Service Unavailable indicating an overloaded server or a generic 500 Internal Server Error — because they either indicate provider-side issues or represent cases where input could be rejected with a more instructive 4xx code. Within Knock's retry logic, most 5xx codes are retryable, so a single request can produce multiple error entries if each retry also fails. We believe this accurately represents the provider's availability during those periods.
Channel growth
In Knock, a connection to a provider API is modeled as a channel. Growth rank (1st through 10th) reflects how many new channels were created for each provider during the 90-day window. To detect directional trends, we split the window into two 45-day halves and compare them, producing the trend indicators (up, down, or stable) shown alongside each rank.
Public incidents and status page updates
On provider detail pages, we integrate with each provider's public status page via RSS or API and overlay reported incidents on the performance data we collect. Our view is that a severe degradation in measured performance should correspond to a status page entry, and the degree of correlation between observed metrics and public incidents is a useful signal for how a provider handles incident management. Incidents are not inherently negative — status page updates paired with observed degradation are indicators of engineering discipline.
Pricing estimates
When modeling pricing curves and cost-per-email estimates, we select the lowest-cost plan that covers a given sending volume. This means we optimize purely for volume — we do not factor in premium features like dedicated IPs, advanced analytics, or priority support that may only be available on higher-tier plans. If a provider offers multiple plans at the same volume level, we use the one with the lower base price. Overage rates are applied on top of the included email allowance for each plan. The result is a floor estimate of what each provider costs at a given volume, making it straightforward to compare providers on price alone.
Frequently asked questions
Which email provider has the lowest API response time?
Based on real-world data from 500M+ messages sent through Knock from December 13th to March 13th, SendGrid has the lowest median API response time at 22ms (p50). The top three by response time are SendGrid (22ms), Postmark (33ms), Resend (79ms).
Which email provider is the most reliable?
Amazon SES currently has the lowest error rate at 0.00% for 5xx responses and timeouts. The top three by reliability are Amazon SES (0.00%), Mailgun (0.00%), Mailjet (0.00%). Knock automatically retries failed requests across all providers.
Which email provider is the most popular?
By volume on the Knock platform, SendGrid leads with 500M+ messages from December 13th to March 13th. The top three by volume are SendGrid (500M+), Mailgun (100M–500M), Amazon SES (25M–100M).
Which email provider is growing the fastest?
Resend currently ranks 1st in growth among 10 providers tracked on the Knock platform. The top three fastest-growing providers are Resend, SendGrid, Amazon SES.
Which email providers offer a free tier?
9 of the 10 providers tracked here offer a free tier: Amazon SES (3,000 emails), Mailersend (500 emails), Mailgun (3,000 emails), Mailjet (6,000 emails), Mailtrap (4,000 emails), Postmark (100 emails), Resend (3,000 emails), SendGrid (3,000 emails), Sparkpost (500 emails). Free tier limits vary, and some providers impose daily rather than monthly caps.
Can I use multiple email providers with Knock?
Yes. Knock enables you to integrate any combination of email providers into a single notification workflow. You can route between providers, run migrations, or use different providers for different message types, all without changing your application code.
Use any of these providers with Knock
Knock enables you to integrate any combination of email providers into a single notification workflow. Manage templates, orchestrate cross-channel delivery, and switch providers without changing your code.