Why your bought prospect list bounced

You bought a list. Five thousand contacts, delivered in minutes, and the month looked promising.

Then you sent to it. A large share bounced, several replies told you the person left two years ago, and your open rates dropped on the next campaign as well.

That last part is the expensive one. The bad list did not just waste a send. It damaged the sending reputation you use for every send after it.

Here is what actually went wrong.

1. The data was old before you bought it

Contact data decays constantly. People change jobs, companies restructure, email formats change after acquisitions, and businesses close.

How fast is a genuinely contested question, and the disagreement is worth seeing:

• MarketingSherpa's widely cited figure is about 2.1% per month, compounding to roughly 22.5% a year. (IndustrySelect)
• ZoomInfo's 2026 analysis puts annual contact decay at 25 to 30%. (ZoomInfo Pipeline)
• Some vendor studies claim rates as high as 70% a year. (Landbase)

Be careful with the high end. As one benchmark review notes, the most-cited data quality numbers circulate so widely that their original source is often lost, which is how a plausible figure becomes an unverifiable one. (Derrick)

The conservative figure is enough to make the point. At 22.5% a year, roughly a fifth of any list is wrong within twelve months of being assembled.

The underlying driver is simply that people move. US median employee tenure is 4.1 years, and shorter in technology. (Bureau of Labor Statistics) One job change invalidates the title, the email, and the direct dial at once.

Most list vendors do not rebuild their database for each order. They query a stored dataset assembled over months or years. The record you receive may have been accurate when collected and wrong by the time it reached you.

The question to ask a vendor is not how large their database is. It is when each record was last verified.

2. Verification was skipped or faked

There is a real difference between three things that get described the same way:

Format checking. Confirming an address looks like an email address. This catches typos and nothing else.

Pattern guessing. Assuming firstname.lastname@company.com because that is the company pattern. Often right, frequently wrong, never verified.

Actual verification. Checking with the receiving mail server that the specific mailbox exists.

Many lists are sold as verified when only the first two were done. If a vendor will not tell you which method they used, assume the cheapest one.

3. Catch-all domains were counted as valid

Some company mail servers accept every message sent to their domain regardless of whether the mailbox exists. These are catch-all domains, and they cannot be truly validated without an actual delivery attempt. They represent over 10% of addresses in some datasets. (Landbase)

A vendor padding volume marks every catch-all address as valid, because technically nothing rejected it. You find out the truth when your replies never come and your bounce rate climbs slowly rather than immediately.

An honest list flags catch-all addresses separately so you can decide whether to send to them.

4. The titles were wrong

This costs more than bounces and gets discussed less.

An email can be perfectly valid and still be useless because the person does not do the job you think they do. Titles vary enormously between companies. A Head of Operations at a twelve person company and at a two thousand person company are different buyers with different budgets and different problems.

Filtering by title string alone produces lists that are technically accurate and commercially worthless.

What bouncing actually costs you

This is the part most buyers underestimate.

A bounce rate above 2% damages your reputation with mailbox providers and puts future sends at risk of the spam folder. (Litmus)

Since February 2024, Google and Yahoo have enforced requirements on bulk senders including SPF, DKIM and DMARC authentication, one click unsubscribe, and a spam complaint rate below 0.3%. Microsoft followed with enforcement from May 2025, rejecting non compliant bulk mail outright rather than routing it to junk. (MarTech)

Practitioners generally advise managing to 0.1% and treating 0.3% as an emergency ceiling, because once you cross it, recovery is slow and depends on sustained good behaviour. (Red Sift)

A bad list does not cost you one campaign. It costs you the channel for weeks.

How to check a list before you send

Do this before your first send, not after.

Sample fifty records at random. Not the first fifty, which are often the cleanest.

Check each one manually. Does the company still exist? Does the person still work there? Does their actual role match what the list claims?

Run the sample through a verification service. Compare the result to what the vendor claimed.

Count catch-alls separately. If the vendor did not flag them, they inflated your valid count.

If more than a handful of the fifty fail, the remaining four thousand nine hundred and fifty will fail at a similar rate. Do not send to it.

The smaller list is usually the better one

The instinct when buying data is to maximise volume for the price. That instinct is what vendors optimise against.

Four hundred verified contacts at the right companies in the right roles will outperform five thousand unchecked rows, and it will not cost you your sending domain.

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References

1. IndustrySelect, Measuring the High Cost of Bad Contact Data — industryselect.com
2. ZoomInfo Pipeline, B2B Data Decay — pipeline.zoominfo.com
3. Landbase, Data Decay Rate Statistics — landbase.com
4. Derrick, B2B Data Quality Benchmarks 2026 — derrick-app.com
5. US Bureau of Labor Statistics, Employee Tenure Survey — bls.gov
6. Litmus, Email Deliverability Rules — litmus.com
7. MarTech, Bulk email restrictions from Google, Yahoo and Microsoft — martech.org
8. Red Sift, Bulk email sender requirements — redsift.com

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We build verified prospect lists monthly, with every contact checked before delivery and catch-all addresses flagged rather than counted. See Growth Partnership.