Verifying a Million-Row List: Which Tools Handle It, and the Cost

Verifying a million addresses cost between $449 (MillionVerifier) and $3,199 (ZeroBounce) on vendors' October 2026 pricing pages, and took from under an hour to about six hours by their own documentation. File limits decide which tools can take the list in one piece: ZeroBounce and MillionVerifier can, DeBounce needs five or more files.

Before comparing tools, it helps to know what you are uploading. So we built one.

How big is a million-row CSV?

We generated two synthetic files of 1,000,000 addresses each on 1 October 2026, using a Python script with a fixed random seed. Addresses were shaped like first.last@domain (some with a number), spread across the four largest consumer providers and 20,000 made-up business domains.

File	Columns	Raw size	Gzipped
Email only	1	28.8MB	10.4MB
Typical lead export	email, first name, last name, company	56.6MB	17.2MB

A real CRM export with twenty or thirty columns will be several times larger. The point is that even an email-only million-row file is bigger than several vendors' per-file or per-request limits.

File limits and processing speed

From each vendor's documentation, as of October 2026:

Vendor	Per-file or per-request limit	Stated speed	Source
ZeroBounce	1GB, up to 500 columns	1M in about 45 minutes or less (popular domains); about 5 hours or less (mixed domains)	docs
MillionVerifier	1 million emails and 100MB per file; XLSX 150,000 rows	3,000 a minute default; 1M in about 6 hours	upload, speed
DeBounce	20MB and 200,000 emails per file	Not stated	help
Bouncer (API)	100,000 emails per batch; 60 batches a minute	Not stated	API
Emailable (API)	50,000 emails per batch	Not stated	API
NeverBounce (API)	25MB per request; split over 1M into 1M chunks; 10 concurrent jobs	Not stated	guidelines
Mailgun (API)	25MB per file, CSV or gzip; 5 jobs in parallel	Not stated	bulk docs

Reading the two tables together:

• ZeroBounce and MillionVerifier take a million-row file in one upload, as long as a MillionVerifier file stays under 100MB, which a lean export will.
• DeBounce needs at least five files at its 200,000-row cap.
• Mailgun's 25MB limit is smaller than our raw email-only file, but it accepts gzip, and the gzipped version was 10.4MB. Compress before you upload.
• NeverBounce's API enforces a 25MB payload limit, and its guidelines ask you to split anything over a million into one-million chunks and run each as a separate job.
• Bouncer and Emailable batch APIs need 10 and 20 batches respectively for a million.

Speed depends on domains, not just volume

Both speed claims come with a condition. ZeroBounce gives two figures, because consumer providers answer quickly and small business servers do not. MillionVerifier warns that files made mainly of one or two domains "may experience automatic speed reduction of up to 90%".

That second point catches B2B teams. A million-row list concentrated on a handful of large companies, or a consumer list that is mostly one provider, will run far slower than the headline rate, because mail servers throttle repeated connections from the same source. Verifiers slow themselves down rather than get blocked.

MillionVerifier also notes that it runs two uploaded files at a time by default and splits speed between them. Splitting a million rows into ten files does not make it ten times faster.

Cost at one million

Prices for a one-off million from each vendor's pricing page, read on 1 October 2026:

Vendor	1,000,000 addresses	Per 1,000
MillionVerifier	$449	$0.45
DeBounce	$750	$0.75
Reoon	$960	$0.96
Verifalia (Standard)	$1,490	$1.49
Bouncer	$2,000	$2.00
Emailable	$2,100	$2.10
Kickbox	$2,999	$3.00
ZeroBounce	$3,199	$3.20

Pricing pages: MillionVerifier, DeBounce, Reoon, Verifalia, Bouncer, Emailable, Kickbox, ZeroBounce. EmailListVerify's public packs stop at 100,000; NeverBounce's pricing page returned HTTP 403 to us; Mailgun's published validation bands stop at 500,000 ($1,820 for the first 500,000).

At this volume the spread is about seven to one. Billing rules move the real figure: ZeroBounce says it removes duplicates and malformed rows without charging, Bouncer says it does not charge for duplicates or unknowns, Reoon does not charge for unknowns, and MillionVerifier refunds results it cannot verify with certainty. On a million rows, a few percent of duplicates is tens of thousands of credits.

A practical process for a million rows

1. Deduplicate first. Lower-case the addresses, trim whitespace and remove exact duplicates before you upload. Do not rely on the vendor; you pay for whatever their rules do not catch.
2. Strip columns you do not need. Keep an ID and the email, verify, then join results back to the full record. Smaller files stay under caps and upload faster.
3. Price it before you split it. Our verification cost calculator compares a one-off million against your monthly volume, which can change which vendor makes sense.
4. Compress if the tool accepts it. Gzip cut our email-only file by nearly two thirds.
5. Sample before you commit. Verify 5,000 random rows. If the invalid share is very high, the list may not be worth sending to at all, and you have saved most of the bill.
6. Split by vendor limits, not arbitrarily. Follow the documented cap (200,000 at DeBounce, 1 million at MillionVerifier) and name files so results rejoin cleanly.
7. Plan around the slow domains. If a few domains dominate, expect the slowdown described above and do not schedule a send the same afternoon.
8. Handle the uncertain rows separately. Send to confirmed-valid addresses first. Treat catch-all and unknown results as a separate, smaller, later send. Should you email catch-all addresses? has a framework.

Which tool for which million

Situation	Fits best
Lowest cost, can wait a working day	MillionVerifier
Need it done within an hour, mostly consumer domains	ZeroBounce (by its own stated times)
Low cost, happy to split into files	DeBounce
Pushing through an API pipeline	Bouncer or Emailable batch endpoints
Want deeper retries on slow servers	Verifalia High or Extreme, at 2 or 4 times the credits

Disclosure — our product

SimpleVerifier, which publishes this blog, is not built for this job. Its throughput is 45 addresses a minute and CSVs are capped at 100,000 rows, so a million addresses would take ten uploads and about 15 days of continuous processing. For a one-off million-row clean, use one of the tools above. It is priced at $29.99 a month flat for steadier, smaller volumes; see /pricing.

The takeaway

For a million rows, price, file caps and domain mix matter more than any accuracy claim. Deduplicate and slim the file, sample before paying for the whole thing, and pick a vendor whose documented limits fit the file you actually have.