Why Did I Get an "Unknown" Result?

An "unknown" result means Mailthentic couldn't get a definitive answer from the mail server. Here are the most common causes and what to do about them.

Common Causes

1. Server Timeout

The mail server didn't respond within the timeout window (15 seconds per command). This can happen with overloaded servers or servers in distant geographic regions.

2. Connection Refused

The mail server refused the connection entirely. This could indicate:

• The server is temporarily down.
• Our IP was temporarily blocked by the server's firewall.
• The server doesn't accept connections from unknown senders.

3. Temporary Errors (4xx responses)

The server returned a temporary error like:

• 450 — "Try again later" (often greylisting).
• 451 — "Temporary local problem."
• 452 — "Too many recipients" or "Insufficient storage."

Mailthentic retries these automatically, but if all retries fail, the result is marked as unknown.

4. STARTTLS Required

Some servers require encrypted connections and may reject unencrypted attempts. Mailthentic supports STARTTLS, but rare configurations may still cause issues.

What to Do

1. Wait and retry. Most "unknown" results resolve if you re-verify after a few hours. The mail server may have been temporarily overloaded.
2. Re-verify the next day. If the issue persists, try again after 24 hours.
3. Check the domain. If you consistently get "unknown" for all addresses at a specific domain, the domain's mail server may be particularly restrictive.
4. Treat persistent unknowns as risky. If an address returns "unknown" after multiple attempts over several days, treat it as risky for sending purposes.