Sendex sits beside Kickbox's result, not in place of it. Kickbox first sorts each address into deliverable, undeliverable, risky or unknown, and it treats accept-all, disposable and role addresses as kinds of risky (docs.kickbox.com/docs/terminology, read 24 September 2026). The Sendex score then grades the address on a sliding scale from 0 to 1.
Read the two together. The result answers whether the mail server accepted the address. Sendex answers a softer question: how much the address looks like one a real person uses and reads. A deliverable address at a free-mail domain can score lower than a deliverable address that follows a company's naming pattern, because the score blends in signals beyond the SMTP reply.
Where does it help? Mostly inside the risky bucket. If you must choose which accept-all addresses to send to first, a higher Sendex score is a reasonable tie-break. For deliverable addresses it's a fine-tuning tool, and undeliverable ones should go no matter what they score. Sendex is Kickbox's own scale, so compare scores within Kickbox results only.
ZapBounce takes a different route to the same decision. Instead of one blended score, each row shows its working: the result, a reason such as accept_all_domain or mailbox_not_found, the literal smtp_code from the mail server, and separate role, disposable and free_provider flags. You can filter on exactly the signal you care about. The result codes reference lists every value.
Pricing sits on a different scale too. Kickbox charged $10 for 1,000 checks and $70 for 10,000 on 24 September 2026, with credits expiring one year from purchase. ZapBounce charges $5 for 1,000 and $25 for 10,000, credits never expire, and unknown results are never billed. See ZapBounce vs Kickbox for the full terms.
Related questions
What is a good Sendex score?
A higher Sendex score means a better-quality address on Kickbox's 0 to 1 scale. Kickbox's terminology docs describe the scale in full. Use the score to rank addresses inside the same Kickbox result, not to overrule an undeliverable verdict.
Is Sendex the same as the Kickbox result?
No. The result says whether the address is deliverable, undeliverable, risky or unknown. Sendex is a separate 0 to 1 quality score built from signals like role accounts and free-mail domains.
Does ZapBounce give a quality score like Sendex?
ZapBounce shows the underlying signals instead: the result, a reason code, the mail server's smtp_code and the role, disposable and free_provider flags. You filter on each one directly in your download or API response.
Does Kickbox charge for unknown results?
No. Kickbox refunded unknown results when its site was read on 24 September 2026. ZapBounce never bills unknown results or duplicates.