---
title: "Kickbox vs EmailShield: What \"Valid\" Actually Means"
description: "We compared Kickbox vs EmailShield: Kickbox refunds the credit when a result is unknown, EmailShield spends the credit resolving it. Here is the gap."
canonical: "https://emailshield.co/alternative/kickbox-alternative"
last-updated: "2026-09-03"
---

> We compared Kickbox vs EmailShield: Kickbox refunds the credit when a result is unknown, EmailShield spends the credit resolving it. Here is the gap.

EmailShield [EmailShield](https://emailshield.co/)

Blog

# Kickbox vs EmailShield: What "Valid" Actually Means

July 18, 2026By [Levi Nagy](https://emailshield.co/authors/levi-nagy)

[Levi Nagy](https://emailshield.co/authors/levi-nagy)

Head of Operations & Client Success

EmailShield is the most accurate email verification tool available, at one of the best prices in the market — 99.8% accuracy at $19/mo for 10,000 credits. Kickbox is a strong, straightforward pick for teams that want a prepaid credit pack, a refund-on-unknown policy and a sender-risk score in the same platform.

- EmailShield. Best for outbound teams, cold-email senders, email marketers, SDR teams, agencies and RevOps who would rather pay to resolve a catch-all or Microsoft 365 address than get the credit back with the question still open.

- Kickbox. Best for teams that want a refund when a result cannot be reached, plus a Sendex sender-risk score.

The choice turns on one axis: what happens after a verifier can't give you a definitive answer.

## The comparison at a glance

| Dimension | EmailShield | Kickbox |
|---|---|---|
| Accuracy | 99.8%, measured across 8.19M+ addresses verified in production | 95% guaranteed |
| Starting price | $19/mo (Starter, 10,000 credits) | $5 for 500 credits (prepaid, no subscription) |
| Free tier | 40,000 credits, 7-day trial, no card | 100 verifications on signup |
| Verification method | Live SMTP handshake on every address, avg 4.5 probes per verdict | Verification API; method not publicly detailed |
| Unknown-result handling | Large share resolved via M365 API and catch-all classification | Refunds the credit |
| M365 API-level verification | Yes; 23.5% of all verdicts resolve this way | Not published |
| Catch-all handling | Domain-level classification with a confidence score; 160,845 domains fingerprinted | Returns "unknown" |
| Spam-trap screening | 7 heuristics, 0.65-1.0 confidence, forced invalid at 0.75+; pristine traps remain undetectable | Not attempted, by stated policy |
| Sender-risk score | Not offered | Sendex score on every address |
| Billing on invalid + duplicates | Free | Not published |
| Credit expiry | Never expire; survive cancellation | Do not expire |
| Published methodology | 10-category verdict taxonomy, 12-stage pipeline | Not published |
| Best for | Outbound teams, cold-email senders, email marketers, SDR teams, agencies and RevOps who want unknowns resolved, not refunded | Teams wanting a refund policy and a sender-risk score |

Kickbox figures verified 24 July 2026 from kickbox.com/pricing, kickbox.com/email-verification-api and Kickbox's resource centre.

## Verified pricing snapshot

| Vendor | Tier / pack | Price | Per verification | Cost per usable address | Billing unit |
|---|---|---|---|---|---|
| EmailShield | Starter, 10,000 credits | $19/mo | $0.0019 | $0.0025 | Subscription; invalid + duplicates free, top-ups never expire |
| EmailShield | Plus, 100,000 credits | $49/mo | $0.00049 | $0.00064 | Subscription; invalid + duplicates free, top-ups never expire |
| EmailShield | Scale, 1,000,000 credits | $249/mo | $0.000249 | $0.00033 | Subscription; invalid + duplicates free, top-ups never expire |
| Kickbox | 500 credits | $5 | $0.01 | n/a — unknowns refunded, not billed | Prepaid pack |
| Kickbox | 10,000 credits | $70 | $0.007 | n/a — unknowns refunded, not billed | Prepaid pack |
| Kickbox | 100,000 credits | $500 | $0.005 | n/a — unknowns refunded, not billed | Prepaid pack |
| Kickbox | 1,000,000 credits | $2,999 | $0.002999 | n/a — unknowns refunded, not billed | Prepaid pack |

Sources: emailshield.co/pricing and kickbox.com/pricing, verified 24 July 2026. Usable-address math applies one list composition (15.6% unknown/protected, 8.4% catch-all) from Q3 2026 EmailShield platform data; it normalizes pricing rather than measuring accuracy. Kickbox's cells are marked n/a because it refunds the credit on an unknown rather than billing it — a different and genuinely fair mechanism, not a worse one.

EmailShield is cheaper at every published tier. Kickbox's per-email price falls as volume rises, from $0.01 at 500 credits to $0.003 at a million, but the top-end gap is $249 against $2,999, and it repeats every cycle a team re-verifies.

## EmailShield at a glance

EmailShield runs its own self-hosted SMTP verification infrastructure: live handshakes against the recipient's real mail server for every address, an average of 4.5 probe attempts per final verdict with each retry from a different egress IP, and zero third-party verification API calls. Across 8.19M+ verified addresses and 37.1M+ SMTP handshakes, 22.3% of a typical B2B list comes back definitively invalid and 15.6% unknown or protected. (For the mechanics, see [how email verifiers work: SMTP vs. DNS](https://emailshield.co/blog/how-email-verifiers-work-smtp-vs-dns/).)

The distinguishing move is what happens to that 15.6%. Catch-all domains are probed at the domain level first, using up to five plausible-but-nonexistent addresses built to look like real typos; a domain that accepts everything gets classified catch-all with a confidence score rather than a guess. Eight perimeter gateways are fingerprinted (Proofpoint, Proofpoint Essentials, Mimecast, Barracuda, Cisco IronPort, Symantec/Messagelabs, Forcepoint, Trend Micro).

None of this is billed as extra: syntactically invalid emails and duplicates cost nothing, and a top-up credit unused this month is still usable next year, subscription or no subscription. Current tiers are at [emailshield.co/pricing](https://emailshield.co/pricing/).

## Kickbox at a glance

Kickbox is a prepaid, credit-pack verification API with no forced subscription. Pricing is fully public, no signup gate: 500 credits for $5, 1,000 for $10, 5,000 for $40, 10,000 for $70, 100,000 for $500, 250,000 for $1,500, up to 1,000,000 for $2,999. Credits do not expire.

Kickbox's clearest differentiator is its refund policy: when it cannot provide a definitive result, it refunds the credit — a rare and genuinely good practice in a category where most vendors quietly bill for whatever they cannot classify. Every verified address also receives a Sendex score, Kickbox's proprietary sender-risk rating, a real capability with no EmailShield equivalent. Kickbox also explains candidly why it does not attempt spam-trap detection: pristine traps cannot be reliably identified by any verifier, and trying risks false positives and privacy problems. That is an honest, defensible position, not a gap Kickbox is hiding.

## Resolving unknowns compared

Both vendors agree that a definitive answer is sometimes impossible. The difference is what happens next.

Kickbox's mechanism is a refund. When it can't produce a definitive result — most commonly on a catch-all domain — it returns the credit rather than billing it. That is fair to the buyer's wallet. It is not, however, an answer: the address is still unclassified, and the sender still has to decide whether to mail it, exclude it, or push it through another tool. (See [what catch-all verification means](https://emailshield.co/blog/catch-all-email-verification/).)

EmailShield's mechanism is resolution. Catch-all domains are checked at the domain level before per-address probing starts, which is why 160,845 domains (7.7% of the 2.09M profiled) already carry a catch-all classification with a confidence score instead of a blank "unknown." Addresses on Microsoft 365 — 35.9% of B2B mailboxes, and only 51.4% valid over plain SMTP versus 90.6% on Google Workspace — get checked at the API level instead, and that single path accounts for 23.5% of every verdict EmailShield issues. Gateway-fronted addresses get the same domain-aware treatment, because 30.1% of them resolve to catch-all and a flat SMTP answer would be wrong.

A refund protects the budget; a resolved verdict lets a sender act. For a list that is 15.6% unknown or protected, that compounds fast.

## What each vendor publishes about accuracy

EmailShield publishes 99.8% accuracy, measured in production across 8.19M+ verified addresses and 37.1M+ live SMTP handshakes, at an average of 4.5 probes per final verdict across 2.09M+ domains profiled — Q3 2026 platform data.

Kickbox publishes a 95% accuracy guarantee and refunds the credit when it cannot reach a definitive result. Worth noting on its own terms: 95% is more modest than the roughly 99% figures most of the category leads with, and a lower published number more plausibly reflects honest measurement than a weaker product. That restraint is to Kickbox's credit. (For how the SMTP handshake works, see [email verification vs. validation](https://emailshield.co/blog/email-verification-vs-validation/).)

One distinction worth drawing for anyone comparing verifiers generally: an SMTP 250 response is not proof of deliverability. A beta client once brought EmailShield a list a legacy verifier had marked 100% valid; the campaign still bounced 7%, enough to trip Google's 2% threshold. Part of that list sat on catch-all domains where a 250 had been counted as proof of existence, and part on Microsoft 365, where SMTP alone is unreliable. That is the failure mode domain-level catch-all classification and API-level M365 verification exist to close.

## Spam-trap screening

Kickbox states plainly that it does not identify spam traps, because they cannot be identified systematically and accurately. That is a correct and candid position. Pristine spam traps — addresses seeded to look like real ones, with no public trace — are genuinely undetectable by any verifier, EmailShield included.

What EmailShield runs instead is pattern screening, not trap detection: 7 heuristics covering known trap domains (Project Honey Pot, Spamhaus, SpamCop), typo-trap domains (gmial.com, hotmial.com), wildcard patterns, hex-string local-parts and gibberish local-parts, each scored 0.65 to 1.0, with anything at 0.75 or above forced to invalid. That catches recycled traps, typosquats and synthetic addresses carrying a structural fingerprint. Kickbox's candour about the limit is accurate, and it applies to EmailShield's heuristics too.

## The Verdict Taxonomy

EmailShield publishes ten distinct verdict categories, each with a stated meaning and a recommended action, so "unknown" is never quietly folded into "valid" and a resolved address discloses how it was resolved.

| Category | Meaning | Action for the sender |
|---|---|---|
| valid | Mailbox existence confirmed by live SMTP handshake | Safe to send |
| accepted | Confirmed deliverable via a provider path, such as Microsoft 365 API verification | Safe to send; provenance disclosed, not disguised as an SMTP result |
| catch_all | Domain accepts all recipients; individual existence unprovable | Send with caution or segment separately |
| role | info@, sales@, support@ and similar | Higher complaint risk; exclude from cold outreach |
| disposable | Temporary or burner domain | Remove |
| spam_trap | Matches trap heuristics | Remove immediately; one hit can affect domain reputation |
| inbox_full | Mailbox over quota, will soft-bounce | Retry later or remove |
| disabled | Account suspended or deactivated by the provider | Remove |
| invalid | Definitively rejected | Remove |
| unknown | Server refused a definitive answer after the full retry chain | Do not count as valid |

There is no separate "safe" bucket absorbing ambiguous results. The valid/accepted split exists so a sender can see whether an address was confirmed by a direct SMTP handshake or a provider-level check. Every result carries a confidence score, from 0.4 on a greylisted response to 0.97 on an explicit rejection. The rejection database holds a further 5,810 disposable domains, checked before any probe is spent.

## Where Kickbox wins

Kickbox earns real credit on several fronts. It publishes a guaranteed accuracy number rather than staying silent, and at 95% that number is more modest than most of the category claims — restraint that reads as honest measurement. The refund-on-unknown policy is rare and genuinely buyer-friendly. Its public admission that it does not detect spam traps, with the reasoning stated, is more candid than most vendors manage. The Sendex sender-risk score is a real capability EmailShield does not offer, and Kickbox operates US and EU infrastructure.

None of that changes the resolution argument. Neither a refund nor a risk score turns an unknown catch-all address into a labeled, actionable verdict — the problem EmailShield's domain-level and M365 API-level checks are built to close.

## Choose Kickbox if...

Choose Kickbox if a refunded credit is enough for your workflow — you would rather get your money back on an unresolved address and make the send/no-send call yourself. Choose it as well if your team actively uses the Sendex sender-risk score, since EmailShield has no equivalent, or if a prepaid pack with no subscription is the only billing shape your finance process will accept.

## Which one fits you

Best for: outbound teams, cold-email senders, email marketers, SDR teams, agencies and RevOps with a Microsoft 365-heavy ICP. If your list skews mid-market and enterprise, a meaningful share sits on M365, where SMTP-only checks are unreliable on roughly half the addresses.

Best for: anyone sending through or around security gateways. Behind Proofpoint, Mimecast, Barracuda or IronPort, 30.1% of addresses resolve to catch-all; domain-level probing turns that into a scored result instead of an unknown.

Best for: high-volume senders. At 1,000,000 verifications, EmailShield's Scale plan runs $249 against Kickbox's $2,999 pack.

Best for Kickbox: low-volume, occasional cleans. If you clean a list twice a year and a handful of refunded credits is an acceptable outcome, Kickbox's prepaid pack and refund policy work well.

## Where EmailShield Fits

EmailShield is the most accurate email verification tool available, at one of the best prices in the market: 99.8% accuracy, $19/mo at 10,000 credits, invalid addresses and duplicates free, credits that never expire. It resolves a meaningful share of the unknown slice through domain-level catch-all classification and M365 API-level verification rather than refunding the question back to the sender. If your list runs heavy on M365 or gateway-fronted domains, [talk to the team at emailshield.co](https://emailshield.co) or start with 40,000 free credits and run your own list.

## FAQ

Is Kickbox worth it in 2026? Kickbox is worth using if you value its refund-on-unknown policy and its Sendex sender-risk score, which EmailShield does not offer. If you want unknowns turned into answers rather than refunds, EmailShield resolves more of that slice: M365 API-level verification alone accounts for 23.5% of its verdicts.

Is EmailShield or Kickbox cheaper? At 10,000 verifications, EmailShield Starter is $19 ($0.0019 each) against Kickbox's $70 pack ($0.007). At 100,000, EmailShield Plus is $49 ($0.00049) against Kickbox's $500 pack ($0.005). At 1,000,000, EmailShield Scale is $249 ($0.000249) against Kickbox's $2,999 pack ($0.002999). EmailShield is cheaper at every published tier, verified July 2026.

Does Kickbox charge for unknown results? No. Kickbox refunds the credit when it cannot reach a definitive result — a genuinely good, uncommon policy in this category. The tradeoff is that a refunded credit still leaves the address unresolved. EmailShield spends the credit differently: catch-all domains get a confidence score and Microsoft 365 addresses are checked at the API level, so much of what would otherwise be unknown comes back as an actionable verdict instead of a refund.

Do EmailShield credits expire? EmailShield's top-up credits never expire and continue to work even if a subscription lapses or is cancelled. Kickbox's prepaid credits do not expire either.

How accurate is Kickbox? Kickbox publishes a 95% accuracy guarantee. EmailShield publishes 99.8% accuracy, measured in production across 8.19M+ verified addresses and 37.1M+ SMTP handshakes. Kickbox's 95% is notably more modest than the roughly 99% figures most of the category leads with, and that restraint is to Kickbox's credit.

Does Kickbox detect spam traps? No, and Kickbox says so directly: it does not identify spam traps, because pristine traps cannot be reliably detected by any verifier. That is an honest and correct position. EmailShield runs 7 heuristics (known trap domains, typo-trap domains, wildcard patterns, gibberish local-parts and more) scored from 0.65 to 1.0 confidence, forcing invalid at 0.75 and above, but this screens for trap-shaped patterns; it does not and cannot detect a genuinely pristine spam trap either. No verifier can.

What does catch-all mean in email verification? A catch-all (or accept-all) domain accepts mail to any address regardless of whether the mailbox exists, which makes a per-address SMTP check meaningless. Across 2.09M domains EmailShield has profiled, 160,845 (7.7%) are catch-all, and 30.1% of addresses behind a gateway like Proofpoint or Mimecast resolve that way. EmailShield probes the domain before probing addresses and assigns a confidence score rather than guessing.

Can I verify a Microsoft 365 email address accurately? Microsoft 365 hosts 35.9% of B2B mailboxes, and only 51.4% of those verify as valid over plain SMTP versus 90.6% on Google Workspace, because Microsoft's SMTP frontends often accept RCPT for mailboxes that do not exist. EmailShield checks M365 domains at the API level instead; 23.5% of all its verdicts resolve that way. Kickbox does not publish a separate M365 path.

Does EmailShield have a free trial? EmailShield offers 40,000 free credits on signup with a 7-day trial and no card required. Kickbox offers 100 free verifications on signup, also no card required.

How much does Kickbox cost? Prepaid credit packs only, verified July 2026: 500 credits for $5, 1,000 for $10, 5,000 for $40, 10,000 for $70, 100,000 for $500, 250,000 for $1,500, and 1,000,000 for $2,999. No subscription tier.

## Methodology

Kickbox figures were captured 24 July 2026 from kickbox.com/pricing (the full prepaid ladder, 500 to 1,000,000 credits; there is no subscription view), kickbox.com/email-verification-api (the 95% guarantee) and Kickbox's resource centre (the spam-trap position).

EmailShield's figures (99.8% accuracy, 8.19M+ verified addresses, 37.1M+ SMTP handshakes, 4.5 average probes per verdict, 2.09M+ domains profiled, 23.5% of verdicts resolved via M365 API, 30.1% gateway-catch-all rate, 160,845 catch-all domains, 5,810 disposable domains, 15.6% unknown/protected share) are first-party production measurements from Q3 2026 EmailShield platform data. The cost-per-usable-address column applies that same list composition as a pricing normalization.

Internal links were verified against emailshield.co/sitemap.xml on 25 July 2026. Last updated: July 2026. Citable asset published: Verdict Taxonomy.

By Levi Nagy, Head of Operations & Client Success at EmailShield.

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