InboxPolicy vs ZeroBounce

By Aria Pramesi, founder of InboxPolicy · Updated July 4, 2026

Choose ZeroBounce if you need its spam-trap and abuse-address database or a dashboard for one-off list cleaning. Choose InboxPolicy if you're building an agent that needs a send-decision with SMTP evidence, keyless pay-per-call pricing at $0.01 via x402, and free re-verification within 72 hours.

What's the core difference between InboxPolicy and ZeroBounce?

ZeroBounce checks an address and hands back status fields: valid, invalid, catch-all, spamtrap, abuse, and similar sub-statuses. Your application has to contain the logic that turns those fields into a decision about whether to send.

InboxPolicy runs syntax, MX, and live SMTP checks against its own verification engine, then applies a deliverability policy on top of that evidence. It returns one field: action, set to send, send_with_caution, review, retry_later, or avoid, plus a confidence score and the underlying SMTP evidence. The decision logic lives in the API response, not in your code.

ZeroBounce also maintains a dedicated spam-trap and abuse-address database, something InboxPolicy does not build or claim to match. If spam-trap detection is the primary requirement, that's ZeroBounce's ground.

How does pricing compare?

ZeroBounce's entry price is roughly $8.00 per 1,000 verifications, with a 100-email-per-month free tier and a marketing-oriented dashboard.

InboxPolicy charges $0.01 per fresh verification, paid per call over the x402 protocol in USDC on Base, no account and no API key required. For prepaid use, credit packs are: Starter, $5 for 1,000 credits ($5.00/1k); Builder, $19 for 5,000 credits ($3.80/1k); Growth, $79 for 25,000 credits ($3.16/1k). Volume pricing is available on request.

InboxPolicy has no free tier by design. Free tiers attract list-cleaning abuse, so the $0.01 per-call price functions as the trial. What is free regardless of pack or plan: cache re-verification within 72 hours (returns from_cache, 0 credits), malformed-email rejection before SMTP is attempted (0 credits), and idempotent retries using the same idempotency key (never billed twice).

What do the two APIs actually return?

A ZeroBounce response centers on a status field and sub-status, describing the state of the address as ZeroBounce's engine sees it. Turning that into a send/no-send call is left to the caller.

An InboxPolicy response centers on an action field, already resolved from the SMTP evidence: send, send_with_caution, review, retry_later, or avoid, alongside a confidence score and the raw evidence used to reach it. Nothing is guessed as safe: unknown or catch-all results map to review, not to a default pass. Roughly 30-40% of B2B addresses sit on catch-all domains, so this distinction shows up often in practice.

When should you choose ZeroBounce instead?

• You specifically need spam-trap or abuse-address detection, which ZeroBounce maintains as a dedicated database and InboxPolicy does not offer.
• You want a dashboard-first tool with CSV upload workflows for periodic list cleaning rather than an API embedded in an application or agent.
• A 100-email-per-month free tier matters for testing before committing to paid volume.

When should you choose InboxPolicy instead?

Choose InboxPolicy if you're building an application or agent that needs a decision, not a field to interpret. Specific fits:

• You need a send/no-send action with confidence and SMTP evidence returned in one call, instead of parsing status and sub-status fields yourself.
• You want pay-per-call pricing with no account or API key: $0.01 per verification via x402, USDC on Base.
• You verify the same address repeatedly and want re-checks within 72 hours to cost 0 credits automatically.
• You're building an AI agent: InboxPolicy ships an MCP server exposing decide_send, verify_email, batch tools, and usage, plus a REST API with idempotency keys, per-item batch results, async batches up to 50,000 emails, and signed completion webhooks.

How accurate is InboxPolicy's verification?

InboxPolicy's prior verification engine showed roughly 90% typical valid-verdict agreement with MillionVerifier across more than 2 million verifications, though agreement varies by vertical and drops as low as 60% in some. This is a directional accuracy signal, not a formal recent benchmark, and it is not a direct comparison against ZeroBounce's engine.

What's structural rather than a benchmark number: InboxPolicy never guesses an unknown or catch-all result as safe. Those cases map to review by policy, every time.

Frequently asked questions