X.3.6 · Mail system
SMTP enhanced status code 2.3.6
Requested priority was changed
X.3.6 means your message was accepted, but the priority you asked for, under the RFC 6710 priority extension, was not honoured. The text after the code gives the priority actually used.
| Registry code | X.3.6 |
|---|---|
| Forms in use | 2.3.6 |
| Registry name | Requested priority was changed |
| Subject | 3: Mail system |
| Permanent or temporary | 2.x.x success |
| Associated basic codes | 250 or 251 |
| Defined in | [RFC 6710] |
What the registry says
The message was accepted for relay/delivery, but the requested priority (possibly the implied default) was not honoured. The human readable text after the status code contains the new priority, followed by SP (space) and explanatory human readable text.
IANA SMTP Enhanced Status Codes registry, X.3.6
The basic codes it travels with
- 250 Requested mail action okay, completed
- 251 User not local; will forward to <forward-path>
In practice
X.3.6 belongs to the SMTP priority extension in RFC 6710, which few public servers support. It is a success code with a note, not a failure: the message was accepted but at a different priority from the one requested. Unless your mail flow depends on priority handling, you can ignore it.
What the sender should do
No action is needed unless delivery priority matters to you. The message itself was accepted.
Would verifying the list have prevented 2.3.6?
No
This reply is about your sending setup, the message or the receiving system, not about whether the address exists, so verifying the list will not prevent it.
Common questions
- What does 2.3.6 mean?
- X.3.6 means your message was accepted, but the priority you asked for, under the RFC 6710 priority extension, was not honoured. The text after the code gives the priority actually used.
- What should I do about 2.3.6?
- No action is needed unless delivery priority matters to you. The message itself was accepted.
- Would an email verifier have caught 2.3.6?
- No. This reply is about your sending setup, the message or the receiving system, not about whether the address exists, so verifying the list will not prevent it.
Sources
- IANA: SMTP Enhanced Status Codes registry (checked 2026-11-05)
- RFC 3463: Enhanced Mail System Status Codes (checked 2026-11-05)
- RFC 5321: Simple Mail Transfer Protocol, section 4.2.3 (reply codes) (checked 2026-11-05)
Registry and provider wording is quoted exactly; guidance is written by the SimpleVerifier Team.
SimpleVerifier Team · Last checked against the sources 2026-11-05