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).

A deliverability data API returns population-level email deliverability benchmarks, such as the invalid, catch-all and unknown rates for a mail provider or country domain, as JSON any product can query. BounceZero's is computed from its own verification corpus, 7.93 million addresses in the April to October 2026 window alone, and is free with attribution.

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

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

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.