X.7.20 · Security or policy
SMTP enhanced status code 5.7.20
No passing DKIM signature found
X.7.20 means the message carried no passing DKIM signature, and the receiver requires one.
| Registry code | X.7.20 |
|---|---|
| Forms in use | 5.7.20 |
| Registry name | No passing DKIM signature found |
| Subject | 7: Security or policy |
| Permanent or temporary | 5.x.x permanent failure: resending unchanged will not succeed |
| Associated basic codes | 550 |
| Defined in | [RFC 7372]; [RFC 6376] |
What the registry says
This status code is returned when a message did not contain any passing DKIM signatures. (This violates the advice of [Section 6.1 of RFC 6376].)
IANA SMTP Enhanced Status Codes registry, X.7.20
The basic codes it travels with
- 550 Requested action not taken: mailbox unavailable (e.g., mailbox not found, no access, or command rejected for policy reasons)
In practice
X.7.20 is the precise code for a missing passing DKIM signature, defined in RFC 7372. Many receivers still use 5.7.1 or 5.7.26 instead. Causes include unsigned mail, a DNS key that does not match the private key, and gateways that change the message after signing. To check, send a test to a mailbox you control and read the Authentication-Results header, which shows whether DKIM passed and for which domain. Look for dkim=pass with your domain.
What the sender should do
Set up DKIM signing for your sending domain and check that signatures survive any gateways in the path.
Would verifying the list have prevented 5.7.20?
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 5.7.20 mean?
- X.7.20 means the message carried no passing DKIM signature, and the receiver requires one.
- What should I do about 5.7.20?
- Set up DKIM signing for your sending domain and check that signatures survive any gateways in the path.
- Would an email verifier have caught 5.7.20?
- 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