5.3.0 bounce: other or undefined mail system status
5.3.0Other or undefined mail system statusPermanent: retrying will not help
554 5.3.0 <user@example.com>: Mail system error
What it means
X.3.0 is "Other or undefined mail system status" in RFC 3463. Subject 3 covers the mail system at the destination: the server software, its storage, and its configuration. Detail 0 means the server did not say which part failed. The address and mailbox were fine as far as it could tell.
You see it from delivery agents and gateways that hit an internal error: an antivirus scanner that crashed on an attachment, a pipe to a program that exited badly, or a backend store that refused a write. Some services also use 5.3.0 when content scanning fails on an unusual MIME structure. Its neighbours give more detail: 5.3.1 (system storage full), 5.3.4 (message too big), and 5.3.5 (misconfiguration).
Most system faults are temporary, so 4.3.0 is often what the receiver sends first, and your queue keeps retrying. A 5.3.0 means the receiver decided this message will not get through, usually because the failure is tied to the content.
Likely causes
- A content or antivirus scanner on the receiving side crashed or timed out on this particular message.
- A local delivery program (ticket system, script, or pipe alias) exited with an error.
- The receiving mail store refused the write for an internal reason.
- A malformed MIME structure triggered a parser error in a gateway.
How to fix it
- Resend once with a simpler message: plain text, no unusual attachments. If that goes through, the content triggered the failure.
- Try sending the attachment as a link or in a common format such as PDF if an archive or rare file type caused the problem.
- Give the recipient’s admin the bounce time and message ID; only their logs show which component failed.
- If you run the receiving system, follow the queue ID through your MTA, filter, and delivery agent logs to find the crashing component.
Checks that apply
- SMTP Diagnostics Confirms the receiving server is up and answering, which narrows the problem to processing after the SMTP session.
- Email Header Analyzer Helps identify the receiving gateway product from earlier messages, useful when you report the failure.
FAQ
- Is 5.3.0 my problem or the recipient’s?
- It is a fault in the receiving system. Your message may be the trigger, but only their admin can fix the component that failed.
- Should I keep resending?
- Resend once with simpler content. Repeated identical attempts will fail the same way.