If you have spent any time researching email verification tools, ZeroBounce is almost certainly on your shortlist. It is one of the most recognized names in the category, it has been around for years, and it bundles a lot of features into one dashboard. For plenty of teams it does the job.
But if you have ever exported a ZeroBounce result and found a stack of addresses tagged “catch-all” or “unknown,” you have run into the exact limit that sends people looking for an alternative. Those are usually the addresses you most need an answer on, and ZeroBounce hands the judgment call back to you. This post breaks down what ZeroBounce does well, where it stops, and how Scrubby handles the same addresses differently.
What ZeroBounce does well
It is worth being fair before getting critical. ZeroBounce earns its reputation for several reasons:
- A broad feature set. Beyond core validation, it offers an email scoring product, an activity data signal, an inbox placement tester, and a blacklist monitor. If you want a single tool that touches many parts of deliverability, it covers a lot of ground.
- Solid deterministic checks. Syntax errors, dead domains, missing MX records, and known spam traps get caught reliably. The first layer of validation is dependable.
- Abuse and complainer flags. It identifies known complainers and abuse addresses, which helps protect your sender reputation on the obvious cases.
- Established integrations. Connectors for major ESPs and CRMs are mature, and the API is documented well enough for engineering teams to wire up quickly.
For a list that is mostly standard mailbox providers, ZeroBounce will return a usable result. The trouble starts with the addresses that actually decide your bounce rate.
Where ZeroBounce stops: the “catch-all” and “unknown” verdicts
Most verification tools, ZeroBounce included, check a mailbox by opening an SMTP conversation with the receiving server and asking, in effect, “does this inbox exist?” On a normal server you get a clear yes or no.
Catch-all domains (also called accept-all domains) break that model on purpose. A catch-all server is configured to accept mail for every address at the domain, whether the mailbox exists or not. So when ZeroBounce asks “does [email protected] exist?”, the server says yes. It would say yes to [email protected] too. The SMTP answer carries no information, so ZeroBounce returns a “catch-all” status and, in the cases it cannot resolve at all, an “unknown” one.
That is technically honest behavior. The problem is what it leaves you holding. Catch-all configurations are extremely common across B2B domains, Google Workspace tenants, and Microsoft 365 setups, which means a large share of your most valuable business contacts lands in that pile. ZeroBounce then pushes the decision back to you:
- Send to them anyway and risk hard bounces against addresses that do not exist, which damages your sender reputation.
- Suppress all of them and throw away real, reachable prospects who simply sit behind a catch-all server.
Neither option is good. You paid for verification and got a shrug on the addresses that matter most. If you want the full mechanics of why this happens, our guide on how to safely navigate risky or catch-all email addresses walks through it in detail.
How Scrubby resolves what ZeroBounce cannot
Scrubby was built specifically to answer the question that standard SMTP verification cannot: is this catch-all address a real, deliverable mailbox or not?
Instead of relying on a single SMTP handshake that a catch-all server will always answer “yes” to, Scrubby uses a different validation path designed for exactly these domains. It evaluates signals that distinguish a live mailbox from a non-existent one, even when the receiving server is configured to accept everything. The result is a clear valid or invalid verdict on addresses that other tools, ZeroBounce included, can only label “catch-all” or “unknown.”
In practice this means:
- The “catch-all” column you used to set aside becomes a real, usable segment.
- Genuine prospects behind catch-all domains stay in your campaign instead of being suppressed by a blanket rule.
- Non-existent addresses behind catch-all domains get filtered out before they ever bounce.
This matters most for B2B senders, where a large portion of target accounts run on catch-all infrastructure. Teams that have made the switch tell a consistent story: recovering reachable contacts that a conventional verifier had written off. Our breakdown of how to verify catch-all emails at scale and unlock 42% more leads covers the numbers behind that recovery.
ZeroBounce vs. Scrubby: a side-by-side view
| Capability | ZeroBounce | Scrubby |
|---|---|---|
| Syntax, domain, and MX checks | Yes | Yes |
| Standard mailbox SMTP verification | Yes | Yes |
| Spam trap and abuse flags | Yes | Yes |
| Catch-all and accept-all resolution | Returns “catch-all” or “unknown” | Returns a clear valid or invalid verdict |
| Decision on risky addresses | Handed back to you | Resolved for you |
| Primary strength | Broad all-in-one deliverability suite | Depth on the hardest-to-verify addresses |
The honest framing is that these tools are good at different things. ZeroBounce is a wide, general-purpose suite. Scrubby is a specialist that goes deeper on the single category that breaks general-purpose verifiers.
When switching to Scrubby is worth it
You do not need to rip out your current process to benefit. Consider Scrubby when:
- Your lists are B2B heavy. The more your prospects sit on company domains, Google Workspace, or Microsoft 365, the more catch-all addresses you are leaving unresolved.
- You see a large “catch-all” or “unknown” segment in your ZeroBounce exports and you are guessing what to do with it.
- Your bounce rate is creeping up despite running verification, because the unresolved addresses are slipping into sends.
- You are suppressing too aggressively and suspect you are throwing away real prospects to stay safe.
A common and effective pattern is to use the two together: run your list through your existing verifier, then send the “catch-all” and “unknown” results through Scrubby to recover the deliverable addresses. You can see how that layered approach plays out in our look at why catch-all email validation is the missing piece in tools like ZeroBounce or NeverBounce.
The bottom line
ZeroBounce is a legitimate, capable tool with a deep feature set, and for clean, consumer-heavy lists it will serve you well. Its limit is structural, not a flaw: a single SMTP check cannot resolve a catch-all server, so it labels those addresses and hands the decision back to you.
If those unresolved addresses represent real revenue, that hand-off is expensive. Scrubby was built to close exactly that gap, turning the “catch-all” and “unknown” pile into a clear list of who you can safely reach. If the catch-all segment in your exports has been quietly costing you leads, that is the part worth fixing first.
Amit S.
Marketing Lead