X.7.17 · Security or policy
SMTP enhanced status code 5.7.17
Mailbox owner has changed
X.7.17 means the recipient mailbox has changed owner since the date you gave in a Require-Recipient-Valid-Since check, defined in RFC 7293. The address now belongs to someone else.
| Registry code | X.7.17 |
|---|---|
| Forms in use | 5.7.17 |
| Registry name | Mailbox owner has changed |
| Subject | 7: Security or policy |
| Permanent or temporary | 5.x.x permanent failure: resending unchanged will not succeed |
| Associated basic codes | 5XX |
| Defined in | [RFC 7293] |
What the registry says
This status code is returned when a message is received with a Require-Recipient-Valid-Since field or RRVS extension and the receiving system is able to determine that the intended recipient mailbox has not been under continuous ownership since the specified date-time.
IANA SMTP Enhanced Status Codes registry, X.7.17
In practice
Require-Recipient-Valid-Since lets a sender say when it last confirmed an address belonged to the intended person. If the mailbox changed hands since then, the receiver can refuse with X.7.17 rather than deliver to a stranger. It protects against recycled addresses. Few receivers implement it, but when it appears, the person you knew no longer holds the address. RRVS is mostly discussed in the context of providers that recycle abandoned addresses.
What the sender should do
Remove the address; the person you knew no longer holds it.
Would verifying the list have prevented 5.7.17?
Partly
The reply is not only about one address, but providers weigh how often a sender hits addresses that do not exist. Removing bad addresses before sending lowers that signal.
Common questions
- What does 5.7.17 mean?
- X.7.17 means the recipient mailbox has changed owner since the date you gave in a Require-Recipient-Valid-Since check, defined in RFC 7293. The address now belongs to someone else.
- What should I do about 5.7.17?
- Remove the address; the person you knew no longer holds it.
- Would an email verifier have caught 5.7.17?
- Partly. The reply is not only about one address, but providers weigh how often a sender hits addresses that do not exist. Removing bad addresses before sending lowers that signal.
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