5.6.1: content 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.
- Standard
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 5.6.1
- 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
5.6.1 Media not supported
What it means
X.6.1 says the media of the message, such as a content type or raw 8-bit or binary data, is not supported by the delivery protocol or by the next server on the path. RFC 3463 calls it useful only as a permanent error, so 5.6.1 is the form you see and the message is returned. It can also come from a gateway into a system that accepts only some kinds of content. Changing the format gets the message through: a different file type, a link instead of the attachment, or standard encoding for every part.
Common causes
- Binary or 8-bit content sent to a server that accepts only 7-bit data.
- A content type the destination system cannot store or display.
- A gateway into a system that accepts only some kinds of content.
How to fix it
- 01Make sure your software encodes attachments (base64 or quoted-printable) instead of sending raw 8-bit or binary data.
- 02Send the file in a more common format, or share it as a link.
- 03Read the reply text for the type the server rejected.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
Related codes
- 5.6.3Conversion 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.
- 5.6.0Message content problem, unspecified.Something about the content of the message made it undeliverable, and the server did not say exactly what.
- 5.3.3Requested feature not supported.The message relies on a feature that the receiving system cannot provide, typically at a gateway that cannot carry it into another mail environment.
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