What this code means
The server permanently rejected the message because it is too big for the specified priority. Do not retry the same attempt unchanged.
Technical meaning
The X.7.16 pattern means that the message is too big for the specified priority. The standard says the condition may be temporary, for example when the server is operating in a mode that accepts only higher-priority messages below a defined size limit. In code 5.7.16, the leading digit assigns the result to the permanent class.
Delivery status
The leading digit 5 denotes a permanent failure of the current attempt. Regardless of a possible later change in server mode, handle 5.7.16 as permanent and do not retry the attempt unchanged. The code alone gives neither the message size, the priority value, nor the applied limit.
- Class
- Permanent failure
- Retry
- Do not retry unchanged
- Suppression
- Check the full context
Retry decision
Operational recommendation: stop automatic and manual retries of the same unchanged message. Consider a new, controlled attempt only after a justified reduction in message size, a valid priority change, or a confirmed change to the server limit; check suppression again first.
Suppression decision
Operational recommendation: do not automatically add an address or domain to a suppression list based on 5.7.16 alone. Inspect the full response, message size and priority, server constraints, and other delivery events, then make the suppression decision according to the confirmed cause and applicable policy.
Common causes
- The message size exceeds the limit applied by the server to the specified priority.
- The server is operating in a mode that accepts only higher-priority messages below a defined size limit.
Diagnostic steps
- Inspect the raw SMTP response or delivery report and confirm the exact code 5.7.16 and a basic reply in the 5xx class; retain the complete response text.
- Correlate the response with the intended message, attempt time and stage, server that returned the code, message size, and specified priority; do not infer missing values from the code alone.
- Use available server logs and policy to check the size limit for that priority and the active operating mode. Stop unchanged attempts, check suppression, and make a new controlled attempt only after a confirmed change.
Actions by owner
Sender
- Do not resend the same message manually; confirm that its content, attachments, and priority are intended, and give the sender administrator the full response.
- Reduce the message or change its priority only when justified by the content and confirmed by an administrator; report the result of the new, controlled attempt.
Sender administrator
- Retain the full response, message size, priority, time, and server that returned the code, stop unchanged retries, and check suppression.
- Use logs and policy to establish the applicable limit and server mode, coordinate a confirmed correction with the recipient administrator or provider, and only then make one controlled attempt.
Recipient administrator
- If you manage the server that returned the code, inspect its logs, active operating mode, and size limits for the specified priority at the attempt time.
- Correct the confirmed configuration problem within your control, or give the sender a safe, precise description of the applicable constraints, and verify the new attempt.
Provider
- If you operate a system involved in the attempt, inspect managed-service logs and the size and priority limits applied at the specified time.
- Correct the confirmed problem in the managed layer, or give the appropriate administrators the precise context needed to resolve it; do not trigger suppression based on the code alone.
Sources and verification
The canonical meaning of X.7.16 and its class assignment were verified against the IANA registry and RFC 2034, RFC 5248, and RFC 6710 as of July 17, 2026. Retry, suppression, diagnostic, and owner-action guidance is presented separately as operational advice; this record contains no provider-specific practice.
- iana-smtp-enhanced-status-codesT0 source
Enumerated Status Codes / X.7.16
- rfc5248T0 source
Section 2.1: registry fields and non-exclusive Associated Basic Status Code
- rfc2034T0 source
Section 4: enhanced status class agrees with SMTP reply class
- rfc6710T0 source
IANA registry reference for X.7.16
Last verified:
