TL;DR
4.7.16 is a temporary size-for-priority condition. Verify the full reply and allowed priority policy, adjust only when approved, and retry with limits; it is not a mailbox validity verdict.
What this code means
X.7.16 states that a message is too big for the priority it specifies. The leading 4 marks the outcome transient, but the code does not define the receiver's size threshold, priority syntax, or whether a later unchanged send will succeed.
Technical meaning
RFC 6710 registers X.7.16 as message too big for the specified priority. This is a relation between message size and the priority context named by the response, not a general maximum-message-size status or proof that content is unsafe.
Delivery status
Class 4 means the current policy or capacity outcome can change. It does not authorize increasing priority, dropping content, or changing traffic classification without checking the receiver and organizational policy.
- Class
- Temporary failure
- Retry
- Controlled retry
- Suppression
- Check the full context
Retry decision
Keep the full response and inspect message size, priority treatment, and destination policy. Make only approved changes, then retry with backoff, idempotency, and a bounded time or attempt limit.
Suppression decision
Do not suppress a recipient from 4.7.16 alone. The condition is message and policy scoped, not independent evidence that the recipient address is permanently invalid.
Common causes
- The message exceeds an allowed size for its current priority treatment.
- A receiver applies temporary priority-aware capacity or policy limits.
- Provider-specific diagnostics add size or queue details beyond the registered code.
Diagnostic steps
- Confirm the exact code, 4xx class, complete diagnostic, size, and transaction stage.
- Identify the configured priority treatment and any receiver-provided policy scope.
- Check approved ways to reduce size or alter handling; do not infer a universal limit.
- Make one bounded retry after a justified policy-compliant change or wait.
Actions by owner
Sender
- Provide the full response and message context instead of manually retrying the same payload.
Sender administrator
- Validate message size and priority configuration against the destination's permitted policy.
Recipient administrator
- If you operate the receiver, verify the relevant size and priority rule and share a safe diagnostic.
Provider
- Correlate repeated conditions by policy scope and offer supported size or queue guidance without overgeneralizing it.
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 6710 — SMTP Extension for Message Transfer Priorities — Defines message transfer priorities and related status codes.
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