Verdicts & reasons
Every validation returns exactly one verdict, plus a machine-readable reason code that explains it. The verdict tells you whether to send; the reason tells you why and what to do next.
The four verdicts
| Verdict | Meaning | What to do |
|---|---|---|
| deliverable | The mailbox exists and accepted mail during the probe. | Safe to send. |
| undeliverable | The address cannot receive mail — bad syntax, no mail servers, the mailbox was rejected, or it is on a do-not-mail/abuse list. | Do not send. Remove or correct. |
| risky | Mail was accepted, but we could not prove the specific mailbox exists — most often a catch-all domain. | Send with caution; monitor bounces. |
| unknown | We could not reach a conclusion — the far end was slow, greylisting us, or throttling. Unknown results are free. | Re-check later; never charged. |
Reason codes
The reason code is a stable, lowercase token attached to every result. It refines the verdict.
| Reason | Verdict | What it means |
|---|---|---|
failed_syntax | undeliverable | The address is not a well-formed email address. |
no_mx | undeliverable | The domain publishes no mail servers (no MX or A record that accepts mail). |
mailbox_not_found | undeliverable | The mail server explicitly rejected the recipient (e.g. 550 no such user). |
disposable | undeliverable | The domain is a throwaway / disposable mailbox provider. |
role_based | risky | A role address (info@, sales@, admin@) rather than a person. |
catch_all | risky | The domain accepts every recipient, so acceptance does not prove the mailbox exists. See Catch-all results. |
complained | undeliverable | The address previously generated a spam complaint. |
suppressed_spamtrap | undeliverable | Known or suspected spam trap — sending risks blocklisting. |
suppressed_abuse | undeliverable | On an abuse / do-not-mail suppression list. |
greylisted | unknown | The server asked us to retry later; no conclusion yet. Free. |
throttled | unknown | The server rate-limited the probe. Free. |
timeout | unknown | The server did not respond in time. Free. |
typo_suggested | — | A likely correction is offered (e.g. gmial.com → gmail.com). |
A verdict describes the address at the moment it was checked. Mailboxes fill up, get deleted, and change providers — which is why lists decay and why re-validation exists.
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