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Resend turns email deliverability metrics into a queryable API surface

Resend’s new Email Metrics API exposes delivery, bounce, complaint, unsubscribe, open and click data with time, domain, broadcast and email dimensions, letting teams build reputation dashboards and automated sender-health alerts without scraping the provider UI.

Reviewed and published by Lars Jansen Updated 5 min read
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Key details

  1. Resend launched the Email Metrics API on August 27, 2026.
  2. The endpoint is `/emails/metrics`.
  3. A request without parameters returns all available metrics for the previous seven days.
  4. Date ranges can extend back to the account’s retained history.
  5. Metrics include delivery, failure, bounce categories, complaints, suppressions, opens, clicks, unsubscribes and corresponding rates.
  6. Results can be filtered or grouped by period, domain, broadcast and email.
  7. Time-series results can use different granularities such as hourly grouping.
  8. Resend positions the API for custom dashboards, reports, sender-health alerts and agent-driven analysis.

What builders should take away

  1. Add bounce, complaint and unsubscribe-rate alerts per sending domain rather than watching only account-wide totals; one compromised or poorly targeted stream can otherwise hide inside aggregate volume.
  2. Keep webhook/event processing for recipient-level state and use the Metrics API for trends, rates and operational monitoring rather than trying to replace one with the other.
  3. Store the thresholds and escalation rules your business actually follows so an agent or dashboard can distinguish informational movement from a sender-reputation incident.
  4. Correlate metric spikes with deployments, list imports, campaigns, authentication changes and provider-specific feedback before deciding on remediation.
  5. If you build customer-facing email tooling on Resend, expose the provider metrics with enough context to show the time range, denominator and sending domain rather than presenting a rate as a universal deliverability score.

What changed

On August 27, 2026, Resend released an Email Metrics API at `/emails/metrics`. With no parameters it returns the available metrics for the previous seven days; callers can choose date ranges up to the account’s retained history, request selected metrics, change time granularity and group results by period, domain, broadcast or individual email. Available measures include sent, delivered, delayed and failed messages; permanent, transient and undetermined bounces; complaints, suppressions and unsubscribes; opens and clicks; and corresponding delivery, bounce, complaint, open, click and unsubscribe rates.

Why it matters

Deliverability monitoring is most useful when it can drive action before inbox placement or sender reputation deteriorates. Resend’s metrics were already visible operationally, but a dedicated queryable API makes them infrastructure: teams can put domain-level complaint and bounce trends into their own dashboards, compare them with provider thresholds, create alerts, or let an agent investigate changes without manual exports. The API does not prove why a deliverability metric moved, so builders still need provider-specific signals, DNS/authentication checks and campaign context to diagnose causes.

The endpoint covers both delivery health and engagement

The API exposes message lifecycle counts such as sent, delivered, delayed, failed and suppressed alongside bounce categories, complaints, unsubscribes, opens and clicks. It also provides rate metrics, which makes it possible to monitor sender-health ratios directly rather than recalculating every numerator and denominator from event logs.

Dimensions make sender reputation operationally inspectable

Results can be grouped by time period, sending domain, broadcast or email. That lets a team distinguish an account-wide change from a single domain or campaign and build hourly or longer-term trend views. Resend says the requested start date can extend as far back as the account retains data.

The API is designed for dashboards, reports and alerts

Resend explicitly positions the endpoint for custom deliverability dashboards, campaign reports and alerts when bounce or complaint rates spike. Its launch example also shows an agent using Resend MCP to plot reputation metrics against Gmail/Yahoo thresholds. The useful boundary is that the API supplies measurement; policy decisions about when to stop a campaign or change a sending domain still belong to the application or operator.

Aggregated metrics complement, rather than replace, event processing

Teams that already consume delivery and bounce webhooks still need those events for recipient-level state, suppression handling and application workflows. The metrics endpoint serves a different purpose: aggregated monitoring and analysis. A resilient email system can use webhooks for state transitions and the metrics API as a second operational view that detects rate-level drift or anomalous patterns.

What to watch next

  • Whether Resend adds mailbox-provider dimensions or inbox-placement signals beyond aggregate delivery events.
  • Longer retention controls and whether historical availability differs materially by plan.
  • Push-based anomaly alerts or threshold configuration inside Resend rather than requiring customers to poll the API.
  • Whether the Metrics API gains finer-grained segmentation without exposing recipient-level privacy-sensitive data.
  • How reliably agent-generated sender-health recommendations distinguish reputation problems from ordinary campaign-mix changes.

Still unclear

  • Delivery and engagement metrics do not directly measure inbox placement or explain the root cause of a reputation change.
  • Available historical range depends on the account’s data-retention window.
  • Open and click metrics can be affected by privacy protections, bot activity and client behavior, so they should not be treated as exact human-engagement counts.

Sources

Direct reading behind this dossier.

2 sources
Email Metrics API
Resend primary/vendor

Primary launch source for the endpoint, metrics, dimensions, date ranges and intended dashboard/alert use cases.

Resend Changelog
Resend primary/vendor

Current product changelog confirming the Email Metrics API release.

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