TL;DR
The message was accepted, but the requested priority was changed: success, not rejection. Note the new priority operationally. Do not retry. Deliverability and list hygiene are unaffected; this status is informational.
What this code means
A priority adjustment at acceptance is what X.3.6 reports under success class 2: the message was accepted for relay or delivery, yet the requested priority was not retained, including an implied default treated as requested. Subject family 3 covers mail-system handling, and the leading digit 2 marks acceptance rather than the temporary or permanent system failures seen in 4.3.x. The human-readable text after the status code carries the replacement priority value per the registry format. The code reports that adjustment but does not prove rejection, invalid recipient status, or that the new priority will affect downstream delivery timing.
Technical meaning
Code X.3.6 means that a message was accepted for relay or delivery even though the requested priority was not honored. The human-readable text after the status code contains the new priority, then SP (a space), then explanatory text.
Delivery status
The leading digit 2 denotes success. Code 2.3.6 reports a priority change when the message is accepted; it does not describe a temporary error, a permanent error, or a rejection.
- Class
- Success
- Retry
- Do not retry unchanged
- Suppression
- Check the full context
Retry decision
Do not retry based on code 2.3.6 alone because the message was accepted. If the workflow depends on priority, inspect the reported new priority and the full event context before making a manual decision instead of resending automatically.
Suppression decision
Do not add the address or domain to a suppression list based on code 2.3.6 alone. The code does not by itself report an invalid recipient; make a suppression decision only after checking other independent events for the message and recipient.
Common causes
- The system accepting the message applied a different priority from the one explicitly requested.
- An implied default treated as the requested priority was not retained, and the system reported a replacement value.
Diagnostic steps
- Inspect the raw SMTP response or report and confirm that the enhanced code is exactly 2.3.6 and that the reply belongs to the success class.
- Read the text after the status code: identify the new priority, the following space, and the explanatory text.
- Compare the reported new priority with the requested or implied default priority, and correlate the response with the correct transaction in the logs.
Actions by owner
Sender administrator
- Treat 2.3.6 as success and do not trigger automatic retry or suppression solely because of this code.
- Retain the requested priority, raw response, and reported new priority so the effect of the change on the sending workflow can be assessed.
Recipient administrator
- If the priority change is unexpected, inspect the receiving system configuration responsible for priority handling.
- Compare the reported new priority with the expected behavior for this transaction and share the findings with the sender administrator.
Provider
- Classify 2.3.6 as success and do not route it into automatic rejection handling.
- Retain the code, new priority, and explanatory text in the raw event so the change can be verified.
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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