# The unknown status URL: https://email-validation.org/docs/statuses/unknown/ Updated: 2026-10-20 > Documentation index: https://email-validation.org/llms.txt **Unknown** means we could not get a definite answer this time. Unknown results are **always free**, including checks that ran out of time, and the action is `retry_later`. ## Why checks end as unknown To check a mailbox we ask the domain's mail server whether it exists. Some servers delay new senders on purpose (greylisting), sit behind anti-spam systems that stop the conversation, are briefly down, or answer too slowly. In each case there is no reliable answer to give, so we return `unknown` and charge nothing. ## What to do - **Retry later.** A second check minutes or hours later often succeeds, especially for `greylisted`, `temporary_error` and `server_unavailable`. Bulk jobs check each address once and finish fast, so re-check the `unknown` rows yourself later (a new job or single checks); they cost nothing the first time. - **Do not retry in a tight loop.** Repeating the same failing check every second will not help, and accounts that produce far more free outcomes than charged ones are slowed down for a while (`429 abuse_throttled`). - **On forms:** accept the address and check it again later; do not block the person. - **`timeout`:** the check did not finish within your `timeout` (at most 15 seconds). A larger `timeout` can help with slow servers. ## Reasons ### Mail server unavailable `server_unavailable`: The mail server refused or dropped our connection, so the mailbox could not be checked. - **Recommended action:** Retry later. Check the address again later; the answer often becomes definite on a second try. - **Credit:** free, always. - **Test address:** `server_unavailable@sandbox.email-validation.org` (free)
Example response ```json { "email": "server_unavailable@sandbox.email-validation.org", "status": "unknown", "reason": "server_unavailable", "action": "retry_later", "account": "server_unavailable", "domain": "sandbox.email-validation.org", "did_you_mean": null, "free_email": null, "role_account": null, "disposable": null, "catch_all_domain": null, "mx_found": null, "mx_record": null, "smtp_provider": null, "domain_age_days": null, "processed_at": "2026-11-02T09:30:00.000Z", "credits_used": 0, "request_id": "req_7Hq2LmX9cV4bN8tR1zK6wD" } ```
### Temporary server error `temporary_error`: The mail server reported a temporary problem while we were checking the address. - **Recommended action:** Retry later. Check the address again later; the answer often becomes definite on a second try. - **Credit:** free, always. - **Test address:** `temporary_error@sandbox.email-validation.org` (free)
Example response ```json { "email": "temporary_error@sandbox.email-validation.org", "status": "unknown", "reason": "temporary_error", "action": "retry_later", "account": "temporary_error", "domain": "sandbox.email-validation.org", "did_you_mean": null, "free_email": null, "role_account": null, "disposable": null, "catch_all_domain": null, "mx_found": null, "mx_record": null, "smtp_provider": null, "domain_age_days": null, "processed_at": "2026-11-02T09:30:00.000Z", "credits_used": 0, "request_id": "req_7Hq2LmX9cV4bN8tR1zK6wD" } ```
### Asked to retry later `greylisted`: The mail server asked us to come back later, which is a common anti-spam delay. - **Recommended action:** Retry later. Check the address again later; the answer often becomes definite on a second try. - **Credit:** free, always. - **Test address:** `greylisted@sandbox.email-validation.org` (free)
Example response ```json { "email": "greylisted@sandbox.email-validation.org", "status": "unknown", "reason": "greylisted", "action": "retry_later", "account": "greylisted", "domain": "sandbox.email-validation.org", "did_you_mean": null, "free_email": null, "role_account": null, "disposable": null, "catch_all_domain": null, "mx_found": null, "mx_record": null, "smtp_provider": null, "domain_age_days": null, "processed_at": "2026-11-02T09:30:00.000Z", "credits_used": 0, "request_id": "req_7Hq2LmX9cV4bN8tR1zK6wD" } ```
### Blocked by an anti-spam system `anti_spam_block`: An anti-spam system in front of the mail server stopped our check before it could finish. - **Recommended action:** Retry later. Check the address again later; the answer often becomes definite on a second try. - **Credit:** free, always. - **Test address:** `anti_spam_block@sandbox.email-validation.org` (free)
Example response ```json { "email": "anti_spam_block@sandbox.email-validation.org", "status": "unknown", "reason": "anti_spam_block", "action": "retry_later", "account": "anti_spam_block", "domain": "sandbox.email-validation.org", "did_you_mean": null, "free_email": null, "role_account": null, "disposable": null, "catch_all_domain": null, "mx_found": null, "mx_record": null, "smtp_provider": null, "domain_age_days": null, "processed_at": "2026-11-02T09:30:00.000Z", "credits_used": 0, "request_id": "req_7Hq2LmX9cV4bN8tR1zK6wD" } ```
### Took too long `timeout`: The check did not finish within the time limit, so we stopped waiting and charged nothing. - **Recommended action:** Retry later. Check the address again later; the answer often becomes definite on a second try. - **Credit:** free, always. - **Test address:** `timeout@sandbox.email-validation.org` (free)
Example response ```json { "email": "timeout@sandbox.email-validation.org", "status": "unknown", "reason": "timeout", "action": "retry_later", "account": "timeout", "domain": "sandbox.email-validation.org", "did_you_mean": null, "free_email": null, "role_account": null, "disposable": null, "catch_all_domain": null, "mx_found": null, "mx_record": null, "smtp_provider": null, "domain_age_days": null, "processed_at": "2026-11-02T09:30:00.000Z", "credits_used": 0, "request_id": "req_7Hq2LmX9cV4bN8tR1zK6wD" } ```
### Check could not finish `internal_error`: Something went wrong on our side while checking this address, so no credit is used. - **Recommended action:** Retry later. Check the address again later; the answer often becomes definite on a second try. - **Credit:** free, always. - **Test address:** `internal_error@sandbox.email-validation.org` (free)
Example response ```json { "email": "internal_error@sandbox.email-validation.org", "status": "unknown", "reason": "internal_error", "action": "retry_later", "account": "internal_error", "domain": "sandbox.email-validation.org", "did_you_mean": null, "free_email": null, "role_account": null, "disposable": null, "catch_all_domain": null, "mx_found": null, "mx_record": null, "smtp_provider": null, "domain_age_days": null, "processed_at": "2026-11-02T09:30:00.000Z", "credits_used": 0, "request_id": "req_7Hq2LmX9cV4bN8tR1zK6wD" } ```