Compared
Unknown versus undeliverable email results
An unknown email verification result leaves the address unsettled. Keep it separate from an undeliverable result so a failed lookup or inconclusive probe does not become an automatic rejection.
| What you want to know | Treat unknown as undeliverable | Keep unknown separate |
|---|---|---|
| Meaning of the result | Treats missing evidence as a reason to reject | Preserves the difference between an inconclusive check and a deterministic failure |
| Greylisting or a timeout | Rejects an address without a mailbox conclusion | Retains unknown and considers a later check for a temporary reason |
| Policy or capability restriction | Marks the address bad even when the probe was restricted | Reads the reason; repeated probes may not resolve the limitation |
| Signup handling | Blocks the person because the check could not settle the address | Follows the action; asks for email confirmation when control matters |
| List handling | Deletes or suppresses an address as if failure were established | Holds it for a separate decision; neither proves delivery nor approves sending |
| Work still in progress | Can mistake pending for an unsuccessful check | Polls pending after the returned interval before handling the terminal result |
What each result establishes
unknown means the available evidence could not settle the address. A timeout, greylisting or a server policy can leave that outcome. undeliverable reflects a deterministic reason to reject under Emvero’s current policy, such as invalid input, DNS_NXDOMAIN for the address domain or an explicit NULL_MX declaration that the domain accepts no mail.
A negative SMTP reply also needs interpretation. An observation classified as SMTP_MAILBOX_NOT_FOUND currently becomes unknown with SMTP_RECIPIENT_REJECTED_AMBIGUOUS. The service does not treat that probe as sufficient proof to reject the address. This is why the returned status, action and reason_codes need to stay together.
Choose the next step from the reason
SMTP_GREYLISTED or SMTP_CONNECT_TIMEOUT can justify a later check. A greylisting response is temporary, but a retry still has no guaranteed outcome. SMTP_POLICY_REJECTED describes a restriction on the session; immediately repeating it may produce the same refusal. Unsupported extensions and blocked destinations need a different response, as the unverifiable address definition explains.
At signup, allow_with_email_confirmation lets you continue with confirmation when mailbox control matters. Your application sends that confirmation email; Emvero’s verification sends none. An unknown result does not certify ownership, delivery or suitability for your service.
In a list workflow, keep unknown addresses in a separate group with their evidence. Decide whether to recheck a temporary condition or hold the address for review. Deleting the group loses addresses the verifier did not establish as bad; automatically sending to it assumes an answer the verifier did not obtain. Provider-level restrictions can affect several addresses together.
pending is work in progress, not a terminal unknown. Poll after the returned interval, then handle the completed result. See the verification result guide for the response fields, and the score versus evidence comparison for why a numeric threshold cannot replace this distinction.
Where this shows up in a result
Reason codes from the closed vocabulary in the API response. These are the exact strings an integration writes an if against.
SMTP_GREYLISTED | Temporary SMTP deferral; a later check may help but does not guarantee a conclusive result. |
SMTP_CONNECT_TIMEOUT | Mail server did not answer in time |
SMTP_MAILBOX_NOT_FOUND | Recipient refusal observed by SMTP; current policy returns unknown with SMTP_RECIPIENT_REJECTED_AMBIGUOUS. |
SMTP_POLICY_REJECTED | Session refused on policy |
Related terms
Greylisting
A receiving-server policy that temporarily defers an unfamiliar SMTP attempt; a later attempt may pass.
Hard bounce and soft bounce
Common labels for permanent and temporary delivery failures; neither label alone explains the cause.
Codes that describe us, not the address
Reasons that explain omitted or incomplete work within Emvero, without establishing a missing mailbox.
Policy rejection
A receiving server refuses an SMTP operation under its security or policy rules; the refusal does not establish a missing mailbox.
Read a verification result.
See an example of status, recommended action and check evidence. Sign in to check your own address.