Standard SMTP codes · permanent error
5.6.5: conversion failed
A server tried to convert the message content so it could be delivered, and the conversion did not succeed.
- Standard
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 5.6.5
- 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
- Either side, depending on the cause. Start with the checks below that are yours.
- What the server says
5.6.5 Conversion Failed
What it means
X.6.5 covers a conversion that was needed and attempted, but failed. RFC 3463 says it can be a permanent or a persistent temporary notice, so you may see 5.6.5 (the message was returned) or 4.6.5 (the server will try again, for instance after a fault is fixed). Typical triggers are corrupt attachments, malformed encodings, or a converter on a gateway that fails on unusual content. Resending the same message usually fails the same way unless the content changes.
Common causes
- A corrupt or malformed attachment that the converter cannot read.
- Broken encoding in the message body or headers.
- A fault in the converting software on the gateway.
How to fix it
- 01Recreate the attachment, or send it in another format.
- 02Rebuild the message with a standard mail client and resend.
- 03For 4.6.5, wait for the retries; if it turns into a bounce, contact the recipient's administrator.
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.
- 5.6.2Conversion needed but not allowed.The content would have to be converted to be delivered, but the message itself or the sending host's policy forbids 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.
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