5.6.0: message content problem, unspecified
Something about the content of the message made it undeliverable, and the server did not say exactly what.
- Standard
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 5.6.0
- Provider
- Standard SMTP codes
- Temporary or permanent
- PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
- Who has to act
- The sender. The fix is on the sending side: your domain, your server or your list.
- What the server says
5.6.0 Other or undefined media error
What it means
X.6.x codes are about the content and its format: content types, encodings and conversions. Detail 0 is the general one. RFC 3463 places content issues under the control of both sender and receiver, which must share a common set of supported content types. Servers may also use 5.6.0 for content they consider malformed, such as a broken MIME structure or headers that break the message format rules. As a 5.y.z code it means the message was returned; a 4.6.0 is uncommon. The reply text usually names the part of the message the server objected to.
Common causes
- A message with a malformed MIME structure or broken encoding.
- Headers that break the message format rules, such as a duplicated or missing required field.
- Content the receiving system cannot process for a reason without its own code.
How to fix it
- 01Read the reply text for the part it objected to.
- 02Send the same message to a mailbox you control and inspect the raw source for broken MIME or headers.
- 03Rebuild the message with a standard mail client or library and resend.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
Related codes
- 5.6.1Content type not supported.The message uses a kind of content that the delivery protocol or the next system on the path cannot carry, so it was refused.
- 5.6.3Conversion needed but not possible.The content has to be converted before it can be passed on, but a server on the path is not able to perform that conversion.
- 5.6.5Conversion failed.A server tried to convert the message content so it could be delivered, and the conversion did not succeed.
5.6.0 at other providers
- 554 5.6.0Malformed message.Gmail refused the message because its structure breaks the Internet Message Format rules of RFC 5322, so it cannot be read reliably.
- 550 5.6.0Moderation fails without an expiry policy tag.A message to a moderated group failed because the approval agent needs a retention tag that the organization has not created.
- 554 5.6.0Attachment scan timed out under a transport rule.A Word or Excel attachment could not be scanned in time by a transport rule set to defer on failure, so the message was returned.
Further reading
All 105 standard codesEvery code in the wikiPaste your own bounce