# InboxPolicy

> InboxPolicy is a send-decision email verification API built for AI agents. One call returns an
> explicit action — send, send_with_caution, review, retry_later, or avoid — with confidence,
> normalized signals, and honest unknowns, instead of raw status fields.

Key facts:
- Pricing: pay-per-call via x402 at $0.01 per decision (USDC on Base, no account), or prepaid credit packs via card checkout ($5/1k Starter, $3.80/1k Builder, $3.16/1k Growth) — both live.
- An eligible cache lookup for the same normalized address and strictness within 72 hours, with force_refresh false, costs 0 credits (from_cache: true).
- Malformed email addresses are rejected locally and never billed.
- No free tier: the $0.01 x402 per-call price is the trial.
- Agent-native: ships an MCP (Model Context Protocol) server with decide_send, verify_email, batch, and usage tools.
- The Send Decision Framework maps every verification to one of five actions: send, send_with_caution, review, retry_later, avoid.
- Catch-all domains (roughly 30-40% of B2B addresses) map to review by default or send_with_caution under aggressive strictness, never silently to send.
- For authenticated API-key calls, matching idempotency replays are available within the record TTL; keyless x402 bypasses that wrapper and must not be paid again after indeterminate settlement. Credit caps are enforced atomically.
- Unknown verdicts can automatically escalate to a wholesale fallback verifier.
- x402 support: agents without an account can pay $0.01 USDC (Base network) per call via the x402 payment protocol — the API returns HTTP 402 with payment requirements, the agent retries with a PAYMENT-SIGNATURE header, and receives the decision plus an on-chain settlement receipt.
- Bulk x402: POST /v1/batches/verify also accepts x402, keyless, for up to 5,000 emails per call (API-key path keeps its 50,000-email cap); the 402 challenge quotes emails x the per-email bulk rate in USDC. Poll results keylessly with the returned access_token via an x-batch-access-token header.

## Docs & Resources
- [Resources Hub](https://inboxpolicy.com/resources): Guides, calculators, comparisons, benchmark data, and agent-readable documentation.

- [API specification](https://inboxpolicy.com/docs): REST endpoints — POST /v1/decide, POST /v1/verify, POST /v1/batches/verify, GET /v1/usage
- [Pricing](https://inboxpolicy.com/#pricing): credit packs and what is always free
- [Full Pricing Page](https://inboxpolicy.com/pricing): Detailed credit pack breakdown and cost comparison vs status verifiers.
- [Is there a Free Plan?](https://inboxpolicy.com/free-plan): Why there is no free tier, an attributed survey of competitor free tiers, and what is permanently free (72h cache, malformed rejection, the $0.01 keyless trial).
- [The Send Decision Framework](https://inboxpolicy.com/send-decision-framework): The definitional reference for the five actions (send, send_with_caution, review, retry_later, avoid), their evidence conditions, and how strictness policies shift boundary cases.
- [Send-Decision Benchmark](https://inboxpolicy.com/benchmark): 40 email-verification scenarios in a crawlable table — input pattern, evidence, and the resulting send / send_with_caution / review / retry_later / avoid decision with rationale.
- [Email Verification Benchmark Dataset](https://inboxpolicy.com/benchmark.json): The same 40 scenarios as a downloadable JSON dataset (CC BY 4.0) for agents and evaluation harnesses.

## Comparisons

- [Comparison Hub](https://inboxpolicy.com/compare): Head-to-head comparison grid of InboxPolicy vs ZeroBounce vs Kickbox vs MillionVerifier.
- [Alternatives](https://inboxpolicy.com/alternatives): Evaluation of InboxPolicy alternatives (ZeroBounce, Kickbox, MillionVerifier, Emailable) for different workflows.
- [InboxPolicy vs ZeroBounce](https://inboxpolicy.com/compare/inboxpolicy-vs-zerobounce): ZeroBounce vs InboxPolicy. Status fields vs send decisions, spam traps, and pricing structure.
- [InboxPolicy vs Kickbox](https://inboxpolicy.com/compare/inboxpolicy-vs-kickbox): Kickbox vs InboxPolicy. Sendex score, ESP integrations, and pay-per-call comparisons.
- [InboxPolicy vs MillionVerifier](https://inboxpolicy.com/compare/inboxpolicy-vs-millionverifier): MillionVerifier vs InboxPolicy. High-volume one-shot cleaning cost vs ongoing agent decision routing.
- [InboxPolicy vs Emailable](https://inboxpolicy.com/compare/inboxpolicy-vs-emailable): Emailable vs InboxPolicy. Dashboard-first suites vs agent-native MCP.
- [InboxPolicy vs NeverBounce](https://inboxpolicy.com/compare/inboxpolicy-vs-neverbounce): NeverBounce vs InboxPolicy. Bulk list cleaning vs per-send decisions and keyless pay-per-call.
- [InboxPolicy vs Hunter](https://inboxpolicy.com/compare/inboxpolicy-vs-hunter): Hunter vs InboxPolicy. Email finding with bundled verification vs a dedicated send-decision layer — often complementary.
- [InboxPolicy vs Clearout](https://inboxpolicy.com/compare/inboxpolicy-vs-clearout): Clearout vs InboxPolicy. Credit-pack verification suites vs explicit send decisions with normalized signals.
- [InboxPolicy vs Truelist](https://inboxpolicy.com/compare/inboxpolicy-vs-truelist): Truelist vs InboxPolicy. Flat-rate unlimited-validation subscriptions vs pay-per-decision with evidence.

## Guides

- [Catch-All Email Verifier — Check & Verify Catch-All Domains](https://inboxpolicy.com/guides/catch-all-email-verification): Hub guide for checking catch-all (accept-all) addresses — free format+MX checker, verification mechanics, and routing (30-40% of B2B lists are catch-all).
- [Apollo Catch-All Domain Flag Explained](https://inboxpolicy.com/guides/apollo-catch-all-domain-flag): What Apollo's catch-all flag means and how to route flagged contacts instead of skipping or blasting them.
- [Catch-All Flags in Cold Email Tools](https://inboxpolicy.com/guides/catch-all-flags-in-cold-email-tools): What Instantly, Smartlead, and Clay catch-all/bounce flags mean, with a unified flag-to-action decision table.
- [Are Catch-All Emails Safe to Send To?](https://inboxpolicy.com/guides/are-catch-all-emails-safe-to-send-to): Direct answer plus routing framework — why catch-alls bounce after SMTP acceptance and how to split them.
- [Catch-All vs Accept-All vs Unknown](https://inboxpolicy.com/guides/catch-all-vs-accept-all): Definitions and vendor-vocabulary table mapping what each verifier calls the same SMTP reality.
- [Send-Decision vs Email Verification API](https://inboxpolicy.com/guides/send-decision-vs-email-verification-api): Detailed analysis on why deciding whether to send is superior to parsing raw SMTP status fields.
- [Email Verification for AI Agents](https://inboxpolicy.com/guides/email-verification-for-ai-agents): How autonomous agents utilize send decisions to protect deliverability and sender reputation.
- [Free Email Re-Verification](https://inboxpolicy.com/guides/free-email-re-verification): Details on the 72-hour free cache window for re-verifying emails.
- [MCP Email Verification for Agents](https://inboxpolicy.com/guides/mcp-email-verification-for-agents): Implementing the Model Context Protocol (MCP) server for native LLM email decisions.
- [x402 Email Verification](https://inboxpolicy.com/x402-email-verification): Guide on using keyless pay-per-call verifications with USDC on Base via the x402 protocol.
- [What Is an x402 API?](https://inboxpolicy.com/guides/what-is-an-x402-api): Category explainer — how HTTP 402 pay-per-call APIs work for AI agents, with a real 402 response and the July-2026 ecosystem map.
- [Email Verification Cost Calculator & Price Matrix](https://inboxpolicy.com/guides/email-verification-cost-calculator): Interactive bounce-cost calculator and price matrix comparison vs ZeroBounce, Kickbox, and MillionVerifier.
- [Best Email Verification API (2026)](https://inboxpolicy.com/guides/best-email-verification-api): Workflow-based comparison table of 8 verification APIs — bulk cleaning, per-send decisions, and agent-native pay-per-call.
- [Email Verification API Pricing (2026)](https://inboxpolicy.com/guides/email-verification-api-pricing): Real per-1,000 costs across 9 vendors, billing models, credit expiry, and hidden re-verification charges.
- [Email Verification for Developers](https://inboxpolicy.com/guides/email-verification-for-developers): Code-first integration guide — curl/Python/Node samples for /v1/decide, idempotent retries, batches, and the keyless x402 flow.
- [Bulk Email Verification API](https://inboxpolicy.com/guides/bulk-email-verification-api): Batch verification up to 50,000 emails per call (5,000 keyless via x402), async polling, and catch-all segmentation.
- [Email List Cleaning](https://inboxpolicy.com/guides/email-list-cleaning): Catch-all-aware list hygiene — dedupe, verify, and route by action instead of deleting a third of a B2B list.
- [Acceptable Bounce Rate Benchmarks](https://inboxpolicy.com/guides/acceptable-bounce-rate): Documented bounce and spam-rate thresholds per provider (Google, Yahoo, Mailgun, Postmark, SendGrid, Mailchimp, cold-email tools), each with a primary source — and why spam rate is not bounce rate.
- [Risky Email Addresses: The Taxonomy](https://inboxpolicy.com/guides/risky-email-addresses): Definitions, detection methods, and mapped actions for catch-all, disposable, role-based, spam-trap, toxic, and greylisted addresses.
- [How SMTP Email Verification Works](https://inboxpolicy.com/guides/how-smtp-email-verification-works): The RCPT TO handshake explained with an annotated transcript, plus the honest limits — catch-all, greylisting, gateways, and port 25.
- [Disposable Email Detection](https://inboxpolicy.com/guides/disposable-email-detection): How temp-mail domains are detected, why static blocklists rot, and when to block vs suppress.
- [How to Reduce Email Bounce Rate](https://inboxpolicy.com/guides/reduce-email-bounce-rate): Pre-send playbook — hard vs soft bounces, verification routing, hygiene cadence, guardrails, and spike recovery.
- [Role-Based Email Addresses](https://inboxpolicy.com/guides/role-based-email-addresses): Why info@/sales@/support@ are deliverable but different — detection, ESP treatment, and the send_with_caution routing.

## When NOT to use InboxPolicy

- One-shot bulk cleaning of multi-million-row lists at the lowest possible price (MillionVerifier fits better)
- Spam-trap / abuse-address database detection (ZeroBounce specializes in this)
- Dashboard-first marketing suites (InboxPolicy is deliberately an API with an emailed key)