Don't verify emails.
Decide if you should send.
One API call answers the question your agent is actually asking: send, review, or avoid — with confidence, evidence, and honest unknowns. Built for AI agents via REST and MCP.
No free tier, no signup. Point your agent's wallet at the endpoint and pay $0.01 per decision. Prepaid credit packs from $5 — card checkout, no crypto needed.
$ curl -X POST https://api.inboxpolicy.com/v1/decide \ -H "x-api-key: ip_live_..." \ -d '{"email": "vp.sales@prospect.com"}' { "action": "send", "confidence": 95, "reason": "Verified mailbox with acceptable risk.", "signals": { "catch_all": false, "disposable": false }, "from_cache": false, "cost": { "credits": 1 } // re-check within 72h: 0 }
What is a send-decision API?
TL;DR: InboxPolicy is an email verification API that returns a send decision — send, send_with_caution, review, retry_later, or avoid — instead of raw status fields. It's live today at $0.01/call via x402 (no account); prepaid credit packs from $5 per 1,000 (card checkout) drop the price to $0.005/check or less. Re-verifying the same address within 72 hours is free, malformed input is rejected locally at no charge, and AI agents can call it natively through its MCP server.
How the send-decision API works
Syntax, MX, and live SMTP checks run against our own verification engine — then a deliverability policy turns the evidence into one action your code can branch on.
One call, one question
POST /v1/decide with an email address. Idempotency keys make retries safe — the same key never bills twice — enforced at the database layer.
Get an action, not homework
Five possible verdicts, each with a reason, confidence score, and the SMTP signals behind it. Unknowns stay honest — we say review, we don't guess "safe".
Fresh lookups only
1 credit per fresh verification. Cache hits within 72h: 0 credits. Malformed emails: 0 credits, rejected before they touch SMTP. Batches dedupe automatically.
The Send Decision Framework: what to do with every verification result
Every verification maps to one of five actions. This is the vocabulary your agent branches on — designed to be safe by default and explicit about uncertainty.
| Action | Meaning | Typical cause | What your agent should do |
|---|---|---|---|
| send | Mailbox verified, acceptable risk | SMTP confirmed, confidence ≥ 70 | Send now |
| send_with_caution | Deliverable but moderate confidence | Confidence 50–70, or catch-all under aggressive policy | Send if the campaign tolerates some bounces |
| review | Cannot confirm the mailbox | Catch-all domain, protective gateway, unknown | Queue for human review or enrichment |
| retry_later | Temporary SMTP condition | Greylisting, transient server issues | Re-check later — the re-check is usually free |
| avoid | Do not send | Invalid mailbox, bad syntax, disposable domain | Drop the address |
The MCP email verification tool for AI agents
InboxPolicy ships a native MCP (Model Context Protocol) server. Your agent gets decide_send, verify_email, batch tools, and live usage as first-class tools — no SDK, no glue code. Add it to any MCP-capable client:
{
"mcpServers": {
"inboxpolicy": {
"url": "https://mcp.inboxpolicy.com",
"headers": { "x-api-key": "ip_live_..." }
}
}
}
The agent asks "should I email vp.sales@prospect.com?" and gets back an action, a confidence score, the SMTP evidence behind it, and what it cost — in one tool call. Decisions your agent can branch on, priced so loops don't hurt: repeats inside the 72-hour window are free.
No API key? Agents can pay per call with x402
InboxPolicy supports the x402 payment protocol: an agent with a wallet can call POST /v1/decide with no account at all. The API responds 402 Payment Required with machine-readable payment requirements; the agent pays $0.01 in USDC on Base per call via the X-PAYMENT header and gets its decision plus an on-chain settlement receipt. Zero signup, zero key management — credit packs stay cheaper ($0.005/check) for sustained volume.
No wallet? Any EVM wallet holding USDC on Base works — most take under a minute to set up. Prefer paying by card? Buy a prepaid credit pack — your API key arrives by email.
Email verification API pricing: how much does it cost?
Pay per call with x402 — $0.01 per decision, in USDC on Base, straight from your agent's wallet. No account, no card, no signup. This is live now.
Pay-per-call (x402)
- Full
decide+verifyAPI, keyless - Free 72h re-verification (cache hits cost $0)
- Malformed emails rejected free, never charged
- Just point your wallet at the endpoint — see the docs
Prepaid credit packs — pay by card, key arrives by email. For sustained volume, prepaid credits run cheaper than per-call ($5.00/1k down to $3.16/1k). No crypto required.
Starter
- Full API + MCP access
- Free 72h re-verification
- Per-item batch results
- Credits never expire
Builder
- Everything in Starter
- Async batches to 50k emails
- Signed completion webhooks
- Automatic fallback on unknowns
Growth
- Everything in Builder
- Priority rate limits
- Volume pricing on request
- Direct support channel
Always free for customers: cache re-verification within 72 hours, malformed-email rejection, and idempotent retries. No free tier: the $0.01 per-call price is the trial — abuse doesn't get subsidized.
InboxPolicy vs ZeroBounce vs Kickbox vs MillionVerifier
Real numbers, July 2026. Different tools win different jobs — here's where each one actually wins.
| InboxPolicy | ZeroBounce | Kickbox | MillionVerifier | |
|---|---|---|---|---|
| Entry price / 1k | ~$10 (at $0.01/call) | $8.00 | $10.00 | ~$0.59–2.50 |
| Output | Decision + evidence | Status fields | Status + Sendex score | Status fields |
| Re-verification cost | $0 within 72h | Full price | Full price | Full price |
| Malformed input | Free, rejected locally | Billed | Billed | Billed |
| Agent-native (MCP) | Yes, first-class | No | No | No |
| Pay-per-call, no account (x402) | Yes — $0.01 USDC | No | No | No |
| Honest unknowns | Preserved + explained | Scored | Scored | Resolved aggressively |
| Spam-trap database | No | Yes | No | No |
| Free tier | No — $0.01/call is the trial | 100/mo | One-time credits | Yes |
When InboxPolicy is not the right email verifier for you
We'd rather you buy the right tool than churn off the wrong one.
One-shot cleaning of a 5M-row scraped list
You want the cheapest bulk status check and don't need decisions. MillionVerifier is the budget king for that job.
Spam-trap and abuse-address detection
That requires a decade-scale curated trap database. ZeroBounce is the specialist there.
Dashboard-first marketing suite
We're an API with an emailed key — deliberately. If your team lives in dashboards and CSV uploads, Kickbox or Emailable will feel more at home.
Frequently asked questions
What is a send-decision API?
A send-decision API verifies an email address and returns an explicit action — send, send_with_caution, review, retry_later, or avoid — instead of raw status fields. InboxPolicy runs syntax, MX, and SMTP checks, applies a deliverability policy, and answers the question agents actually ask: should I send to this address right now?
How is InboxPolicy different from ZeroBounce or Kickbox?
Traditional verifiers return statuses like valid or catch-all and leave the decision logic to you — and they charge for every lookup, including repeats. InboxPolicy returns a decision with confidence and evidence, re-verification within the 72-hour cache window costs 0 credits, and it ships an MCP server so AI agents can call it as a native tool.
What to do with catch-all email addresses?
A catch-all domain accepts mail for any address, so SMTP verification cannot confirm the specific mailbox exists. InboxPolicy marks these honestly — action review (or send_with_caution under an aggressive policy) with the catch_all flag set — instead of guessing. Roughly 30–40% of B2B addresses sit on catch-all domains, which is why the honest handling matters.
Why is there no free tier?
Free verification tiers attract list-cleaning abuse, which damages probe infrastructure and quietly subsidizes spammers. InboxPolicy has no free calls — the $0.01 x402 per-call price is the trial. What's always free for customers: cache re-verification within 72 hours and malformed-input rejection.
How does free re-verification work?
Every fresh verification is cached for 72 hours. Re-checking the same address inside that window returns the cached result — marked from_cache: true in the evidence — and costs 0 credits. Agents that re-validate lists before each send pay only for genuinely new lookups.
How do AI agents use InboxPolicy?
InboxPolicy ships an MCP (Model Context Protocol) server exposing decide_send, verify_email, batch tools, and usage. An agent asks for a decision on an address and receives a machine-readable action with confidence, cost, and evidence in one tool call. The REST API with idempotency keys and per-item batch results covers everything else.
What does an "unknown" result mean?
Unknown means the SMTP conversation couldn't confidently confirm or deny the mailbox — commonly greylisting, a protective mail gateway, or a catch-all domain. InboxPolicy preserves unknown as a first-class state and maps it to review rather than over-promoting it to safe. Unknowns can optionally escalate to a wholesale fallback verifier automatically.
Do you resell or share the email addresses I verify?
No. Addresses are processed to produce your result, cached for 72 hours to make your re-verification free, and subject to retention limits. They are never sold, shared, or used to build lists.
Stop parsing statuses.
Start branching on decisions.
$0.01 per decision, paid from your wallet with x402 — no account, no card, live right now.
Start with x402