timeouts • throttling • retry strategy
Temporary Unreachable Emails
“Temporary Unreachable” is a separate class from invalid. It typically means a verifier could not obtain a reliable signal due to transient behavior like greylisting, throttling, or network timeouts.
Common causes
- Greylisting: server asks the sender to retry later
- Rate limiting: verification bursts get throttled
- Timeouts: slow SMTP responses or network instability
- Temporary mail server issues: transient outage or overload
Why not mark as invalid?
Because a transient failure is not proof the mailbox does not exist. Treating this class as invalid can over-suppress leads and reduce coverage unnecessarily.
Recommended handling approach
| Outcome | Interpretation | Typical action |
|---|---|---|
| Temporary Unreachable | Signal unavailable at time of check. | Retry later / revalidate on a schedule. |
| Repeated Temporary Unreachable | Provider repeatedly blocks reliable signal. | Increase interval, reduce concurrency, or downgrade confidence. |
| Clear invalid evidence | Mailbox does not exist / hard fail. | Suppress from export. |