Every verifier's pricing page leads with a per-email figure. ZapBounce's does too: $5 for 1,000 checks, $25 for 10,000 and $139 for 100,000. That figure tells you what a credit costs. It doesn't tell you what an answer costs, and the answer is the thing you came to buy.
Three billing rules sit between the two numbers. Is an unknown result charged? Is a duplicate row charged? Do unused credits expire? A vendor can quote a low per-email price and still cost more per answer if it bills rows that returned nothing.
Unknown results are where the gap opens. Greylisting, throttling and servers that block probe traffic all end in an unknown, and a B2B list always has some. Of 13 vendors whose billing rules we could read, 8 don't charge for unknowns, and the other five don't publish a rule either way.
Expiry is the quieter cost. Kickbox sells 10,000 checks for $70 and its credits expire one year from purchase (read on kickbox.com, 24 September 2026). Hunter's also expire after 12 months. A credit that lapses is a verdict you paid for and never received. Our answer on credit expiry lists who does what.
Working out cost per usable verdict on one file
Take a 10,000-row upload with 500 duplicate rows and 900 addresses whose servers wouldn't give a straight answer. Say 2,000 of the rest sit on catch-all domains, leaving 6,600 addresses that came back valid or invalid.
ZapBounce bills the 8,600 distinct addresses that got a finding: valid, invalid and catch_all. Duplicates and unknowns are free, and so is a row that fails syntax. At the 10,000 pack's rate of $0.0025 a credit, that's $21.50, or about a third of a cent for each of the 6,600 usable verdicts. The other 1,400 credits stay in your account and never expire.
Run the same file through a vendor that bills every row at the same rate and all 10,000 credits go, $25 for the same 6,600 answers. That works out to about 0.38 cents each, and nothing is left over for your next list.
You can do this sum for any vendor in a few minutes. You need their price, their rule for unknowns and duplicates, and your own list. The rules for each vendor are on which verifiers charge for unknowns, and ours are on the pricing page. The rest of the ZapBounce blog explains each result type in more depth.
Why catch-all sits in the middle
The short version
- Divide what you paid by the valid and invalid results you got back, not by the rows you uploaded.
- Ask every vendor whether unknowns and duplicates are billed, and whether credits expire.
- Count catch-all results on their own line so your cost per decision stays honest.
Questions people ask
What counts as a usable verdict?
A usable verdict is a valid or invalid result: an answer that tells you to send or to remove the address. Catch-all is a real finding about the domain, and unknown means the server gave no answer.
Does ZapBounce charge for unknown results?
No. ZapBounce never bills an unknown, a duplicate row in the same batch, a syntax failure or an error on our side. Valid, invalid and catch_all results each cost one credit.
Do ZapBounce credits expire?
No. ZapBounce credits never expire, so a pack bought for one list covers the next one too. Kickbox and Hunter credits expire after 12 months.
How much does ZapBounce cost per 1,000 emails?
$5 for 1,000 checks, falling to $25 for 10,000 and $139 for 100,000. Every account also gets 100 free credits a month with no card.