Duplicates creep in whenever lists get merged. A CRM export, an event sign-up sheet and last year's webinar list will share dozens of the same people. Checked copy by copy, each repeat would use a credit, and a merged list would cost more than the people on it.
ZapBounce's rule is simple: one credit covers one answer from a mail server, on one distinct address. When the same address appears again in the same batch, that repeat costs nothing. The per-row billed field shows it, and the batch's billed count equals unique addresses minus unknown results and syntax rejects. You can audit the bill against your own file.
Your file comes back whole. Duplicate rows aren't stripped out, because each one may carry different data beside the address: a different owner, source or signup date. Every row keeps its columns, and the result fields sit next to it. Decide in your own sheet which copy to keep, then delete the rest before you import the list back.
The batch summary gives the count at a glance. Alongside valid, invalid, catch_all and unknown, it reports duplicates, role, disposable and billed. A high duplicate count is useful in itself: it tells you your sources overlap, and it's worth fixing at the merge step next time.
Merge before you upload. The free dedupe works within one batch, so combine your sources into a single file first and every overlap is caught in one pass. Then upload it on the bulk page. The rate is $5 for 1,000 checks, unknown results are never billed either, and our duplicate removal guide covers matching beyond exact strings.
Related questions
Do I pay for duplicate emails in email verification?
Not at ZapBounce. A repeat of an address already in the same batch costs no credit. Unknown results and syntax rejects are free too, so you pay only when a mail server gave an answer.
Does ZapBounce remove duplicates from my file?
ZapBounce keeps every row so none of your data is lost. Each repeat is marked in the per-row billed field and counted in the batch summary. Delete the extra copies in your own sheet once you've chosen which record to keep.
Are duplicates across two uploads free?
The free dedupe applies within one batch. Merge your lists into a single file before you upload and every overlap is caught in one pass, at $5 per 1,000 distinct addresses.