5.7.7: message integrity check failed
A system authorised to validate the message found it corrupted or altered, so the check on its integrity failed.
- Standard
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 5.7.7
- 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
5.7.7 Message integrity failure
What it means
RFC 3463 defines X.7.7 for a message whose validation failed because it was corrupted or altered, and allows it as a permanent, temporary or even success code. RFC 7372 names 5.7.7 among the generic codes an operator can keep using instead of the newer authentication codes (5.7.20 to 5.7.26) if it prefers not to reveal its policy. So 5.7.7 can mean a broken signature at a secure messaging gateway, or a failed authentication check reported without detail. Content changed in transit, for example by a forwarder or by a footer added at a gateway, is a common cause.
Common causes
- A server or gateway changed the message after it was signed, for example by adding a footer or rewriting headers.
- Corruption of the message in transit.
- A failed authentication check, such as DKIM, reported with a generic code.
How to fix it
- 01Check whether anything on your sending path modifies messages after signing (footers, link rewriting, disclaimers).
- 02Send a test to a mailbox you control and read the authentication results in its headers.
- 03Sign messages as the last step before they leave your system.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
Related codes
- 550 5.7.20No valid DKIM signature.The receiving server requires a valid DKIM signature and found none that passed verification, so it refused the message.
- 550 5.7.26Multiple authentication checks failed.The message failed more than one authentication check, for example SPF and DKIM, and the receiving server's policy rejects it.
- 5.7.5Cryptographic failure.A system that was authorised to check or decrypt the message could not do it, because a key or other required information was missing or invalid.
Further reading
All 105 standard codesEvery code in the wikiPaste your own bounce