X.7.2 · Security or policy
SMTP enhanced status code 5.7.2
Mailing list expansion prohibited
X.7.2 means you are not allowed to send to that mailing list. The list is restricted to members or approved senders.
| Registry code | X.7.2 |
|---|---|
| Forms in use | 5.7.2 |
| Registry name | Mailing list expansion prohibited |
| 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 3463] |
What the registry says
The sender is not authorized to send a message to the intended mailing list. This is useful only as a permanent error.
IANA SMTP Enhanced Status Codes registry, X.7.2
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.7.2 is returned by mailing list servers and groups that only accept posts from members or moderators. Microsoft 365 uses its own codes for the same situation, 5.7.124 and 5.7.133. Ask the list owner to add you, or reach members individually.
What the sender should do
Ask the list owner to approve your address, or contact members another way.
Would verifying the list have prevented 5.7.2?
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 5.7.2 mean?
- X.7.2 means you are not allowed to send to that mailing list. The list is restricted to members or approved senders.
- What should I do about 5.7.2?
- Ask the list owner to approve your address, or contact members another way.
- Would an email verifier have caught 5.7.2?
- 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