BounceZero - Developer

Deliverability Data API

A free, public API of email deliverability benchmarks - by top-level domain and by mail provider - computed from 10M+ verifications and refreshed each quarter. Built for ESPs, verification tools, CRMs and researchers who want to show or reason about deliverability norms without running a verification network of their own. No key required for the public benchmark endpoints; attribution is required (returned in every response).

What it returns - and what it never will

Every figure is an aggregate, k-anonymized to a floor of 50 distinct domains per cell, and frozen in a versioned snapshot so a value you cache stays reproducible. The API exposes benchmarks by tld (e.g. com, fr) and by provider (e.g. microsoft365). It deliberately does not expose domain-level or address-level reputation - asking "what's the bounce rate for acme.com?" is exactly the query the k-anonymity floor exists to refuse. This is a norms API, not a lookup on anyone's data.

Endpoints

GET /api/v1/benchmark - list available dimensions and values

curl https://bouncezero.io/api/v1/benchmark

GET /api/v1/benchmark/{dimension}/{value} - benchmark for one TLD or provider

curl https://bouncezero.io/api/v1/benchmark/tld/com

{
  "dimension": "tld",
  "value": "com",
  "snapshot": "Q3-2026",
  "domains_seen": 133729,
  "total_checks": 1866845,
  "invalid_pct": 27.9,
  "valid_pct": 62.5,
  "catchall_pct": 4.7,
  "attribution_required": "BounceZero Deliverability Benchmarks, snapshot Q3-2026 (bouncezero.io/email-deliverability-benchmarks-2026)"
}

Fields

invalid_pct - share of checked addresses that were invalid (dead mailbox).
valid_pct - share verified or likely-valid.
catchall_pct - share of checks that hit a catch-all/accept-all response. See the catch-all study for why this needs care.
domains_seen, total_checks - the sample behind the cell (always ≥50 domains).
snapshot - the versioned dataset the figures are frozen in; cite it.

Terms of use

Free to use, including commercially, provided you attribute BounceZero with a visible link to the source research wherever a figure is shown (the exact string is returned in attribution_required). Don't imply BounceZero endorses your product, and don't re-publish the API as your own dataset. It's a v1 public endpoint - no SLA yet, quarterly refresh, snapshots are stable once frozen.

Need per-list verification rather than population benchmarks? That's the core product - verify a list free, or read the validation API docs. The benchmark API here is the free, public companion to our Deliverability Barometer.