TL;DR
The mailbox host is not accepting messages for this attempt. Class 5 makes the unchanged request permanent, but does not prove the address is invalid.
What this code means
5.3.2 applies X.3.2, system not accepting network messages, in the permanent class. The standard lists shutdown, excessive load, and maintenance as examples without selecting one from the code alone.
Technical meaning
X.3.2 concerns the host on which the recipient mailbox resides not accepting network messages. The pattern may describe a permanent or persistent transient error; 5.3.2 is its class-5 result.
Delivery status
The leading 5 marks this unchanged delivery request as permanently failed. It does not show why the host refused messages, prove recipient invalidity, or prove that the host will never accept mail again.
- Class
- Permanent failure
- Retry
- Do not retry unchanged
- Suppression
- Check the full context
Retry decision
Stop automatic and manual retries of the unchanged send. Consider a new attempt only after reliable evidence that the host state or configuration changed.
Suppression decision
Do not automatically suppress the recipient from 5.3.2 alone. This is a host condition; use the full response, event scope, history, and independent address-specific evidence.
Common causes
- The mailbox host was approaching shutdown, under excessive load, or in maintenance, as illustrative standards examples.
- A host configuration or state prevented it from accepting network messages.
Diagnostic steps
- Confirm the exact code, basic reply, host, SMTP stage, time, and raw response.
- Correlate the event with other deliveries to the same host and inspect available sending and destination logs.
- Before another submission, obtain confirmation that the relevant host state or configuration changed.
Actions by owner
Sender administrator
- Stop unchanged retries and retain the complete response and attempt details.
- Give the evidence to the receiving administrator or provider and wait for a confirmed change before a new send.
Recipient administrator
- Inspect the mailbox host, maintenance state, and logs for the reported time.
- Restore message acceptance or communicate the confirmed restriction and verification path.
Provider
- Inspect the operated host's acceptance state and logs for the attempt.
- Correct or explain the confirmed condition without declaring the recipient invalid from 5.3.2 alone.
Sources
These sources define what this enhanced status code means, mainly through the IANA registry and related RFCs. When provider examples appear on the page, they come from that provider's published documentation. Follow the links to read the original wording in context.
- SMTP Enhanced Status Codes — IANA registry of enhanced mail system status codes.
- RFC 5248 — A Registry for SMTP Enhanced Mail System Status Codes — Creates and governs the IANA enhanced status code registry.
- RFC 2034 — SMTP Service Extension for Returning Enhanced Error Codes — Defines how SMTP returns enhanced status codes to clients.
- RFC 3463 — Enhanced Mail System Status Codes — Defines the class/subject/detail model for enhanced status codes.
- RFC 7504 — SMTP 521 and 556 Reply Codes — Defines SMTP reply codes for hosts that do not accept mail.
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