X.7.7 · Security or policy
SMTP enhanced status code 5.7.7
Message integrity failure
X.7.7 means a message's integrity check failed because it was corrupted or altered in transit.
| Registry code | X.7.7 |
|---|---|
| Forms in use | 5.7.7, 4.7.7 |
| Registry name | Message integrity failure |
| Subject | 7: Security or policy |
| Permanent or temporary | 4.x.x persistent transient failure: retrying later may succeed; 5.x.x permanent failure: resending unchanged will not succeed |
| Associated basic codes | Not given |
| Defined in | [RFC 3463] |
What the registry says
A transport system otherwise authorized to validate a message was unable to do so because the message was corrupted or altered. This may be useful as a permanent, transient persistent, or successful delivery code.
IANA SMTP Enhanced Status Codes registry, X.7.7
In practice
X.7.7 appears when a signed message was changed in transit, for example by a gateway that adds a footer or rewrites links after signing. The same mechanism breaks DKIM. Sign as the last step before the message leaves your system.
What the sender should do
Look for a gateway or footer tool that modifies messages after they are signed.
Would verifying the list have prevented 5.7.7?
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 5.7.7 mean?
- X.7.7 means a message's integrity check failed because it was corrupted or altered in transit.
- What is the difference between 5.7.7 and 4.7.7?
- They share the subject and detail digits, so they report the same condition, "Message integrity failure". The first digit is the class: 4.x.x persistent transient failure: retrying later may succeed; 5.x.x permanent failure: resending unchanged will not succeed.
- What should I do about 5.7.7?
- Look for a gateway or footer tool that modifies messages after they are signed.
- Would an email verifier have caught 5.7.7?
- 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)
Registry and provider wording is quoted exactly; guidance is written by the SimpleVerifier Team.
SimpleVerifier Team · Last checked against the sources 2026-11-05