X.7.4 · Security or policy
SMTP enhanced status code 5.7.4
Security features not supported
X.7.4 means the message used security features the delivery path cannot support. As 504 5.7.4 it often means an authentication mechanism the server does not offer.
| Registry code | X.7.4 |
|---|---|
| Forms in use | 5.7.4 |
| Registry name | Security features not supported |
| Subject | 7: Security or policy |
| Permanent or temporary | 5.x.x permanent failure: resending unchanged will not succeed |
| Associated basic codes | 504 |
| Defined in | [RFC 3463] |
What the registry says
A message contained security features such as secure authentication that could not be supported on the delivery protocol. This is useful only as a permanent error.
IANA SMTP Enhanced Status Codes registry, X.7.4
The basic codes it travels with
- 504 Command parameter not implemented
In practice
X.7.4 is often seen as 504 5.7.4 when a client asks for an AUTH mechanism the server does not offer, or uses a security feature the path does not support. Check the mechanisms the server lists in its EHLO reply and use one of those.
What the sender should do
Use an authentication mechanism or security feature the server actually advertises.
Would verifying the list have prevented 5.7.4?
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 5.7.4 mean?
- X.7.4 means the message used security features the delivery path cannot support. As 504 5.7.4 it often means an authentication mechanism the server does not offer.
- What should I do about 5.7.4?
- Use an authentication mechanism or security feature the server actually advertises.
- Would an email verifier have caught 5.7.4?
- 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