greylisted
The server deferred the handshake and asked the sender to come back later
Greylisting answered the probe with a temporary failure. The mailbox is left unverified and the verdict rests on the free signals.
- appears in
- smtp_reason
- credits
- Billed by the verdict it produced: a deliverable answer with smtp_checked false is 1 credit. The settling re-checks are free.
What it means
Greylisting is an anti-spam technique: the first connection from an unknown sender gets a temporary 4xx failure and is expected to retry minutes later. A verification probe cannot wait that long, so smtp_checked is false and mailbox_exists is null.
The verdict comes from everything else Spaw knows about the address, usually deliverable with the unverified weight of 10 added to the risk score and a mailbox_confidence estimate attached.
What to do
Pass callback_url with the lookup: Spaw re-checks the address after 5 and 20 minutes and pushes the settled verdict to you at no cost. Or re-verify later; repeats inside seven days are free.
Example response
{
"deliverable": "deliverable",
"smtp_checked": false,
"smtp_reason": "greylisted",
"mailbox_exists": null,
"mailbox_confidence": 65
}Abbreviated: a real answer carries all 27 fields, listed in the verify-email reference.
Related
- mailbox_full · the mailbox is over its storage quota
- no_mailbox · the server answered that the mailbox does not exist
- disabled · the server reported the mailbox as disabled or suspended
- timeout · the mail server did not answer within the probe's time limit
- no_connect · no mail server accepted a connection on port 25
- mx_unreachable · the mail exchangers could not be reached from the verification network
- delivered_recently · your own delivery report confirmed this mailbox
- provider_unavailable · the verification provider itself could not answer
- All verdict reasons
- Verdicts and the risk score
- API reference
markdown version: /docs/reasons/greylisted.md