Is ZeroBounce Accurate? What Its Results Can and Can't Tell You

What "accurate" means for an email verifier

There is no answer key for a list of email addresses. A verifier can't open the mailbox; it can only ask the server that hosts it. That conversation has four possible outcomes:

The server says	What a verifier reports	How sure it can be
Mailbox exists	Valid	As sure as the server is honest
Mailbox does not exist	Invalid	Very sure
Accepts every address	Catch-all / accept-all	Can't tell from the server
Refuses or times out	Unknown	No answer yet

So when a vendor says it is accurate, the useful question is: accurate on which of these rows? Valid and invalid rows on normal domains are where every competent tool agrees. Catch-all and unknown rows are where tools differ, and where most "my verified list still bounced" stories start. We explain the mechanics in how accurate email verifiers really are.

What ZeroBounce says about itself

ZeroBounce's API page headlines an accuracy guarantee with a specific percentage and a money-back promise. That figure is the vendor's own. We have not seen an independent audit behind it, and we have not seen one behind any other vendor's figure either. That is the reason SimpleVerifier publishes no accuracy percentage at all.

What the page does describe in useful detail is the set of statuses it returns. ZeroBounce says it spots "over 30 email types", grouped roughly like this:

• Valid, with sub-labels such as aliases and alternate addresses.
• Catch-all / accept-all, which it suggests you "further validate with AI Scoring".
• Do not mail: global suppression, toxic, role-based catch-all, MX forward and similar.
• Spam traps, including what it calls pristine and typo traps.
• Invalid: typos, bad syntax, no DNS entries, unroutable IP, does not accept mail.

That breakdown is genuinely useful. A "do not mail" bucket that separates role addresses and known complainers from dead mailboxes lets you make better decisions than a plain valid/invalid split.

Where ZeroBounce, like every verifier, is blind

Catch-all domains

A catch-all server says yes to every address at the domain, real or invented. ZeroBounce labels these rows and sells AI Scoring at 1 extra credit per address to rank them. Scoring of this kind uses signals such as the domain, the name pattern and past activity. It can raise or lower the odds; it can't turn a guess into a confirmation, because the server has already said yes to everything.

On cold B2B lists, catch-alls are often a large slice of the file. Whatever tool you use, treat them as a separate, smaller first batch. See what to do with catch-all emails.

Servers that block verification

Some large providers and security gateways rate-limit or refuse verification probes. Results come back unknown, or they come back accepted and the real rejection happens later. ZeroBounce doesn't charge for unknowns, which is the fair way to handle it.

Time

A check is a snapshot. Someone leaves their job a week after you verify, and the address bounces. No verifier can see that coming, so re-check any list that has sat for more than a few weeks before you send it. The email list decay calculator estimates how much a list has aged.

What it costs to find out

ZeroBounce sells pay-as-you-go credits with a 2,000 minimum. From its pricing page on 6 November 2026:

Credits	Price	Per 1,000
2,000	$39	$19.50
5,000	$69	$13.80
10,000	$129	$12.90
25,000	$274	$10.96
50,000	$499	$9.98
100,000	$649	$6.49
250,000	$1,299	$5.20
1,000,000	$3,199	$3.20

The ZeroBounce ONE subscription starts at $99 a month, with a 10,000-credit minimum. The Freemium plan gives 100 validation credits a month (a business or premium email domain is required). The page says credits never expire while you hold an active ZeroBounce ONE subscription, and that "expiration rules may apply" otherwise. AI Scoring costs 1 extra credit per address. For the full breakdown, see ZeroBounce pricing explained.

How to test ZeroBounce's accuracy on your own list

A vendor's percentage tells you about their test set, not your list. A 30-minute test tells you about yours.

1. Take a sample of 500 rows from the list you actually plan to send. Use the email list sampler so the sample is random, not the top of the file.
2. Run it through ZeroBounce using the 100 free monthly credits, plus a small pack if you need it, and through at least one other verifier.
3. Compare the two files in the verifier comparison tool. Rows where both tools say valid or both say invalid are settled. The rows where they disagree are where the accuracy question lives.
4. Count catch-alls with the bulk catch-all checker. If they are 30% or more of your sample, the "accuracy" of any tool on this list depends mostly on how it handles them.
5. Send only to rows both tools call valid, from a warmed inbox, and count hard bounces over 72 hours with the bounce rate calculator. Under 2% is the usual safe line for cold email.

That last step is the only real accuracy test there is: bounces from your mailbox, on your list.

When ZeroBounce is a good choice

• You want a deep status taxonomy (do-not-mail, toxic, trap types) and will use it.
• You want verification bundled with deliverability tools such as inbox tests and blocklist monitoring.
• You verify occasionally and don't mind the per-credit price at small volumes.

It is a weaker fit if you clean a large list every month: 100,000 credits cost $649 each time you buy them.

Where SimpleVerifier fits

SimpleVerifier takes a deliberately conservative line on the rows nobody can confirm. A catch-all address is always reported risky, never valid, and graded higher, medium or lower likelihood with the reason shown (how the grading works). Unknown rows say why the server didn't answer. Every check is a live SMTP mailbox check, not a syntax pass.

On price, it is built for people who verify every month:

• Pro, $39 a month: Unlimited email verification.*
• Starter, $9 a month: 2,500 emails a month.
• Free: the first 100 checks with a Google sign-in, no card.

*Fair use: the first 100,000 checks a month at full speed, then slower, never cut off.

Pro also includes phone format checks (E.164, country and number type), the email finder, an API with 10,000 calls a month included and an MCP server for AI agents. Compare plans on the pricing page.

The fair way to choose is the test above. Run the same 500 rows through ZeroBounce and through the SimpleVerifier verify page, then let your own bounce count decide.

More reading: is ZeroBounce legit, is ZeroBounce worth it, ZeroBounce vs NeverBounce, catch-all email verifiers compared.