no_mailbox
The server answered that the mailbox does not exist
The detail behind a mailbox_not_found verdict: the handshake reached the recipient check and the server rejected the address outright.
- appears in
- smtp_reason
- credits
- The verdict is undeliverable, so the lookup is free.
What it means
The most reliable negative signal SMTP can give. The server was asked whether it would accept mail for the recipient and said no, usually with a 550 5.1.1 reply. Spaw records mailbox_exists false and the verdict mailbox_not_found.
Only an explicit "no such user" answer maps to no_mailbox. Ambiguous rejections and policy blocks are reported as unverified instead of being guessed.
What to do
Remove the address from the list; it is on your suppression list already.
Example response
{
"deliverable": "undeliverable",
"reason": "mailbox_not_found",
"smtp_reason": "no_mailbox",
"mailbox_exists": false
}Abbreviated: a real answer carries all 27 fields, listed in the verify-email reference.
Related
- mailbox_full · the mailbox is over its storage quota
- disabled · the server reported the mailbox as disabled or suspended
- greylisted · the server deferred the handshake and asked the sender to come back later
- 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/no_mailbox.md