Every email platform keeps a suppression list. When an address hard-bounces, the platform adds it and never mails it again. That's useful housekeeping, and it's also a record of damage already done, because each entry got there by bouncing on a real send.
Those bounces are what platforms and mailbox providers judge you on. Amazon SES recommends a bounce rate under 2%, places an account under review at 5% and says it might pause sending at 10% (SES enforcement FAQ, read 24 September 2026). Mailchimp publishes no figure. Its help centre says suspensions are automatic actions triggered when a single send exceeds industry thresholds.
So the timing is the whole question. A check that runs after the send can only stop the second bounce. A check that runs before the address reaches your platform stops the first one, and the first one is the one that counts.
Some sending platforms, Mailgun and SendGrid among them, include an allowance of validations inside certain sending plans (their pricing pages, read 24 September 2026). The same rule applies to those: they protect you only if you call them before the address reaches a send. Our answer on built-in versus dedicated verifiers goes through the trade in detail.
The two places a check belongs
The first place is the import. Before a purchased, exported or old list goes into your platform, run it through bulk verification. You upload the file, and ZapBounce returns it with your original columns plus a result for every row: valid, invalid, catch_all or unknown. You import only the valid rows, and hold the catch-all ones in their own segment.
The second place is the signup form. A typo such as gmial.com or a throwaway address from a disposable provider enters your list the moment someone submits it. Real-time verification calls POST /v1/verify as the form is submitted and answers while the visitor is still on the page, with a did_you_mean suggestion for the typo. The signup form protection page shows the setup.
Between those two points, your platform's suppression list does the job it's good at. It catches addresses that were valid when you checked them and died later, which is normal decay rather than a data-quality failure.
If you run Klaviyo, the Klaviyo integration covers the export-verify-import loop, and the ZapBounce blog has more on why verified lists still bounce.
Why a suppressed address still matters
The short version
- Verify every list before it goes into your email platform, not after the first campaign bounces.
- Check addresses at the signup form so typos and throwaway domains never enter the list.
- Let your platform's suppression list handle the addresses that decay after you checked them.
Questions people ask
Does my email platform verify addresses before I send?
Most platforms learn an address is bad when it bounces and then suppress it. Some sell or include a validation allowance, which protects you only if you call it before the address reaches a send.
What bounce rate gets an Amazon SES account reviewed?
5%. Amazon SES recommends staying under 2%, places an account under review at 5% and says it might pause sending at 10%, per its enforcement FAQ read on 24 September 2026.
Where should email verification run?
In two places: on a list before it is imported, and on the signup form as each address is submitted. ZapBounce covers the first with bulk file upload and the second with a single-address API call.
How much does it cost to verify a list before import?
ZapBounce charges $5 for 1,000 checks and $25 for 10,000. Unknown results and duplicate rows are never billed, and credits never expire.