Auditing a list somebody sold you
Somebody sold you a list and said it was verified. This page is about testing that claim cheaply, before the first send tells you the answer in a way you cannot take back.
It is also about a risk the audit will not remove, and which matters more than the bounce rate.
The audit tells you about quality, not about safety
Run a sample of a thousand addresses and you will know within an hour whether the vendor's claim holds. A list sold as verified that returns a large invalid share was not verified recently, or at all.
What a high unknown or catch-all share tells you is different and more interesting. It suggests the addresses were generated from name-and-domain patterns rather than collected, because pattern-built addresses cluster on corporate domains where accept-all servers are common.
Here is what the audit cannot do. Purchased lists carry spam traps, and pristine traps are indistinguishable from working mailboxes at the protocol level. No verifier removes them. Hitting one can land your sending domain on a blocklist regardless of how clean the rest of the file looked.
How the work gets done
The order that matters for anyone who bought a list, rather than a generic checklist.
Sample a thousand before paying for the rest
A thousand addresses is $5, or free inside the monthly allowance across two months. That is the cheapest due diligence available on a purchase of any size.
Read the unknown and catch-all share as well as the invalid one
A file that is 40% catch-all was probably assembled from patterns. The vendor's own verification would have reported those as valid, which is how the claim and the reality both stay technically true.
Never send purchased data from your main domain
Whatever the audit says. A separate domain and separate infrastructure means a blocklisting is contained rather than career-defining.
Ramp slowly and watch the first sends
Complaint rate matters more than bounce rate here, because the people on a purchased list did not ask for the mail and some of them will say so.
What verification will not do here
What it costs
A thousand-address sample is $5, and the free hundred a month covers a smaller probe at no cost. Auditing before purchase is the cheapest possible use of this product.
Every tier works the same way. Unknown results and duplicates are never billed, and credits do not expire.
Questions we get asked
The vendor says the list is 98% verified. Can I test that?
Yes, in an hour, on a sample of a thousand. Ask which denominator their figure uses: a number computed after the unknowns and catch-alls are removed can be honest and still describe very little.
Does verifying make a purchased list safe to send?
No. It reduces the bounce rate and leaves the spam-trap risk exactly where it was, because no verifier can see a pristine trap.
What share of invalid should worry me?
Anything above a few percent on a list sold as verified means it was not, or the verification is old. The unknown and catch-all shares tell you more about how it was built.
Try it on your own list first
100 free checks a month, no card. Run a sample and read the unresolved count before you decide anything.