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5.7.7 bounce: message integrity failure

5.7.7Message integrity failurePermanent: retrying will not help

Typical wording
554 5.7.7 Message integrity failure

What it means

X.7.7 is “message integrity failure” in RFC 3463: a check showed that the message was altered or corrupted after it was protected. In practice that means a signature (S/MIME or PGP) that does not verify against the content received.

Gateways that enforce signed mail between partners return it when they cannot verify a signature. The usual reason is that something on the path rewrote the message: a disclaimer footer, a link-rewriting filter, a line-wrapping relay or a transfer-encoding change.

DKIM failures are a separate matter with their own codes (5.7.20 to 5.7.22) from RFC 7372, although the root cause, modification in transit, is often the same. A 4.7.7 is uncommon, since a modified message stays modified.

Likely causes

  • An outbound disclaimer or signature footer added after the message was signed.
  • A security filter that rewrites links or attachments in signed messages.
  • A relay that converted 8-bit content to quoted-printable after signing.
  • Message corruption by a broken relay or storage system.

How to fix it

  1. Send a signed test message directly to yourself and verify it; if it fails, your own system is altering it.
  2. Apply disclaimers and footers before signing, or exempt signed messages from footer rules.
  3. Encode the message as 7-bit (quoted-printable or base64) before signing so no relay needs to change it.
  4. If the recipient’s gateway is altering mail before verification, send them the bounce and the test result.

Checks that apply

  • Email Header Analyzer Shows the path the message took and any filters that stamped it, helping you find the hop that changed the content.
  • DKIM Check Confirms your DKIM selector and key, so you can tell an S/MIME integrity problem apart from a DKIM one.
See the example diagnosed

The classification runs without network lookups and we never store your paste.

FAQ

Is 5.7.7 caused by my email footer?
Quite often. A footer added after signing changes the body, and the signature no longer matches.
Does this mean the message was tampered with by an attacker?
Almost never. Legitimate rewriting by filters and relays is the usual cause.

All 191 bounce codes