ZapBounce and Instantly
Instantly includes verification, and it is worth understanding what that check does before deciding whether a second pass earns its cost.
The bundled check is a filter. It catches dead domains and malformed addresses quickly and cheaply, at the volume Instantly operates at. The question is what it does with the addresses that need a live handshake to resolve.
Built-in verification is a filter, not a verdict
A verification step bundled into a sending platform has to be fast and cheap at that platform's volume. That shapes it toward syntax, MX lookups and cached results rather than a live SMTP handshake with a catch-all probe per address.
The catch-all segment is where that matters. A domain that answers 250 for every address cannot be resolved at all, and a check that does not probe for accept-all behavior will report those addresses as fine. Around 28% of a B2B list sits on such a domain.
For Instantly the stakes are the warmed mailbox fleet. Those domains took months to build, and a segment of unconfirmable addresses sent as though it were confirmed is exactly what burns them.
How the data moves
Verify before the lead list is uploaded
Between your scraper or data source and Instantly. Uploading then relying on the bundled check means the platform has already accepted the list.
Split the upload by verdict
One campaign for confirmed addresses on your best domains, a separate campaign for catch-all on domains you can afford to risk.
Hold the unknowns back
An unknown result means a receiving server refused to answer, often temporarily. Re-check in two weeks rather than committing a warmed mailbox to it.
Re-verify anything that has been queued for weeks
A list verified in March and sequenced in May is not the list you verified. Outbound data decays fast.
Setting it up
- Verify the lead file before it is uploaded to Instantly.
- Split the results into three files: valid, catch-all, and everything unresolved.
- Upload the valid file to your primary campaign on your best-warmed domains.
- Upload the catch-all file as a separate campaign on domains you are willing to risk, with a slower ramp.
- Hold the unknown file and re-verify it in two weeks.
- Watch the bounce rate per campaign rather than per account, so the catch-all experiment gives you a real number.
Instantly: common questions
Instantly already verifies. Why pay twice?
Compare them on the same sample and look at the unresolved count, not the valid count. A check that returns almost no catch-alls is not probing for them.
Should I send to catch-all addresses at all?
As a separate campaign on separate domains, with a slow ramp. Then the bounce rate is information rather than an incident on your main fleet.
What bounce rate burns a domain?
Past 5% you are being treated as a sender who does not maintain a list. On warmed cold-email domains that reputation is the asset you cannot rebuild quickly.
Check a Instantly export today
100 free checks a month, no card. Unknown results and duplicates are never billed.