Why an email verification result is "unknown"

unknown

The verification could not reach a reliable answer. The address is neither confirmed nor rejected.

What it means

Unknown is not a polite word for invalid. It means the mail server did not give a usable answer: it did not respond in time, could not be reached, asked to try again later, or reported a temporary problem with the mailbox.

Some mail servers do this on purpose to slow down spammers, and corporate gateways often answer slowly. That is why a share of unknown results is normal in any list, especially for company domains.

Unknown results do not use a credit, so verifying them again later costs nothing extra until you get a definitive answer.

Reasons that lead to it

• timeout: the mail server did not answer in time.
• no_connect: the mail server could not be reached.
• temporarily_blocked: the server greylisted the check and asked to try later.
• exceeded_storage: the mailbox is full.
• unexpected_error: something failed during the check.

What to do

• Do not treat unknown as valid or as invalid. Decide by risk: for a cold campaign, leave unknown addresses out or send to them in a small, separate batch; for a signup form, accept the address and confirm it by email.
• Verify again later. Timeouts and greylisting often turn into a definitive answer after a few hours.
• Watch the share of unknown in a list. If it is high for a single domain, that domain's server is probably blocking verification, and the answer will not improve by retrying in a loop.

Example API response

{
    "email": "jane.doe@example.com",
    "result": "unknown",
    "reason": "timeout",
    "disposable": false,
    "accept_all": false,
    "role": false,
    "free": false,
    "user": "jane.doe",
    "domain": "example.com",
    "mx_record": "mx1.example.com",
    "mx_domain": "example.com",
    "safe_to_send": false,
    "did_you_mean": "",
    "success": true,
    "message": "Processing time: 812 ms",
    "http_code": "200"
}

Try it without an account: the API has a free sandbox key, eev_sandbox_key, that returns fixed answers for test addresses such as valid@, invalid@, unknown@ and catchall@sandbox.easyemailverification.com.

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