Email Verifier Bounce Guarantees: What They Actually Cover (Read Before You Rely on One)

Several email verifiers publish a bounce guarantee, and buyers often treat it as proof of quality. Read the conditions first. Every guarantee we read covers only hard bounces on addresses the tool marked valid, sent within 24 hours to 7 days of verification, and backed by a full export of your bounce logs. Two of them require an opt-in list, which rules out most cold email, and one excludes Gmail, Outlook and other freemail. The payout is a refund of verification fees, not compensation for a burned domain.

SimpleVerifier does not offer a bounce guarantee. This post sets out what the others actually promise, so you can weigh them properly.

The guarantees side by side

Read from each vendor's own page on 2 November 2026. Terms change, so check the live page before you rely on one.

	MillionVerifier	NeverBounce	ZeroBounce	Emailable
Source	Help page	Guarantee page (updated 5 Apr 2024)	ZB Guarantee	Guarantee page (updated 16 Nov 2023)
Threshold	Hard bounce rate above 4%	Bounce rate above 3%	Below its stated accuracy thresholds	Below its stated deliverability thresholds
Send window	Within 7 days of verification	Within 72 hours	Within 72 hours	Within 24 hours
Minimum list	Not stated	500 unique addresses	1,000 emails	1,000 unique addresses
Results covered	"OK" addresses only	Valid only (not accept-all, unknown, disposable)	The _valid.csv only, with toxic and disposable removed	"Deliverable" only
List source	Not stated	Not stated	Must be opt-in, not purchased	Must be from your own opt-in source
Freemail	Not excluded	Gmail, Hotmail, Outlook, AOL, Yahoo and similar excluded	Lower threshold for AOL, Yahoo and Office 365	Lower threshold for Microsoft-managed addresses
Bounce type	Hard only	Must be invalid; reputation and technical bounces excluded	Hard only; spam content, blacklisted IPs, throttling and configuration excluded	Invalid address only; reputation, misconfiguration and unavailability excluded
Evidence	Detailed hard/soft bounce report, and access to your sending account	Job ID, send time, categories sent, full mailing export with bounce responses	Full mailing export with actual SMTP codes and messages	Contact support within 72 hours of the discrepancy
Other limits	Professional third-party sender required; not for single API checks
Payout	Your last payment refunded	The difference refunded	5% of validation cost per 1% below threshold	100% refund for qualifying emails

What the fine print means for cold email

"Opt-in only" excludes most cold lists

ZeroBounce's terms say the list "must be an opt-in list that you collected and not purchased from a 3rd party". Emailable's say addresses "must originate from an email list consisting of emails you collected from your own opt-in source." A list exported from Apollo, scraped from Google Maps or bought from a data vendor does not meet either. If cold email is your use case, these two guarantees probably do not apply to you.

Excluding freemail removes the hardest addresses

NeverBounce excludes mail sent to freemail providers, "such as, but not limited to, Gmail, Hotmail, Outlook, AOL, or Yahoo", because they have "a high propensity of false bounces." That is honest, and it also means the guarantee does not cover the addresses where verifiers disagree most. Microsoft's consumer domains are a known weak spot for every verifier, ours included.

Short send windows suit one-off blasts, not sequences

A 24-to-72-hour window fits a newsletter that goes out the day after cleaning. A cold sequence that sends step 1 this week and step 4 three weeks later falls outside it for most of its sends. MillionVerifier's 7 days is the most generous of the four, and it still does not cover a month-long sequence.

"Hard bounce on an invalid address" is narrower than "bounce"

All four exclude bounces caused by your reputation, blocklists, content, throttling or server problems. In cold email, a large share of "bounces" are blocks: 550 5.7.x policy rejections, 554 Blocked from gateways, Microsoft's 451 4.7.650 deferrals that eventually expire. Those do not count. Before you file a claim, sort your bounces. Bounce Doctor separates bad addresses from blocks so you know which part of your bounce rate a guarantee could even cover.

You need full logs, and sometimes account access

ZeroBounce wants "the actual SMTP Codes and messages of the bounces, not your email sender classifying it as a bounce." MillionVerifier requires a detailed hard/soft breakdown and access to your sending account. Many sequencers show a bounce count but make full SMTP responses awkward to export. Check that yours can produce them before you count on a refund.

The payout is small next to the real cost

A refund of the verification fee is a few dollars to a few hundred. The real cost of a bad send is a paused campaign, a warmed inbox that needs weeks to recover, or a domain you have to retire. No guarantee covers that. Our post on what to do after a high bounce rate covers the recovery.

Is a guarantee still worth something?

Yes, as a signal. A vendor that writes down a threshold is committing to something, and the exclusions tell you what it is confident about. NeverBounce excluding freemail and ZeroBounce and Emailable setting lower thresholds for Microsoft addresses all say the same thing: Microsoft and freemail are hard for everyone.

But a guarantee is not a substitute for testing. A verifier that marks fewer rows valid will find it easier to meet a guarantee. A verifier that calls catch-alls "valid" will find it harder. Neither tells you which tool keeps more of your list sendable without bounces.

What to do instead

1. Run a sample of your own list through each candidate. 500 rows from the actual source you will send to is enough to see differences.
2. Compare results row by row with the verifier comparison tool to see where the tools disagree and why. Usually the gap is catch-all policy.
3. Send a small batch of each tool's "valid" rows from a healthy inbox and count hard bounces. Our bench test guide explains how to do it fairly.
4. Count kept leads, not just bounces. A tool that marks half your list risky can show a low bounce rate and still cost you pipeline. The catch-all verifiers comparison covers that trade-off.
5. Ask about charges for unknowns. Whether you pay for rows a tool cannot verify matters more over a year than a refund you may never qualify for. See email verification credits explained.

Where SimpleVerifier stands

We do not offer a bounce guarantee, and our fees are non-refundable once charged, as the terms say. What we do instead:

• Valid means a server confirmed the mailbox. Catch-all, role and unconfirmable rows come back risky with a reason, never valid, so the valid file is the part you can send with confidence.
• Rows we could not check are not charged. They come back as couldn't-check, to retry later.
• You can test before paying. The first 100 checks are free with a Google sign-in on the verify page. Pro is $39 a month with the first 100,000 checks a month at full speed, then slower, never cut off. Plans are on the pricing page.

If a written guarantee is a hard requirement for your team, the vendors above are the ones to look at. Read their current terms against your list first.