5.4.300: message expired and the report could not be returned
The message was not delivered in time because the destination did not respond or an error occurred, and the report could not reach the sender.
- Microsoft
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 5.4.300
- Temporary or permanent
- PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
- Who has to act
- Either side, depending on the cause. Start with the checks below that are yours.
- What the server says
5.4.300 Message expired
What it means
Microsoft's table gives 5.4.300 the same short description as 4.4.7, Message expired, with more detail: the message was not delivered in time, because the destination server did not respond or because an error occurred, and the nondelivery report could not be delivered to the sender. Microsoft gives no further guidance for this code, so treat it like any other expiry: check whether the destination is reachable and whether its MX record is correct, then send again.
Common causes
- The destination server did not respond during the delivery window.
- An error stopped delivery, and the report to the sender also failed.
How to fix it
- 01Send the message again; if it succeeds, the failure was temporary.
- 02If it fails again, check the destination's MX record and ask the recipient whether their server is working.
- 03Admins: use message trace to see the delivery attempts and the last error the destination returned.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- Email nondelivery reports and SMTP errors in Exchange Onlinelearn.microsoft.com
Related codes
Further reading
All 111 Microsoft codesEvery code in the wikiPaste your own bounce