FA-76787 / Email MIME structure / Member archive

Inject a mailing-list footer without breaking the message: only mixed is extended · case 02

Signed or encrypted containers get an extra part inserted, invalidating their structure.

Member previewVariant 2 · 3 implementations · 7 checks per implementation

Case contract

A top-level text/plain body in 7bit, 8bit or quoted-printable (default 7bit, case-insensitive) gets the footer appended in place ("text+footer"). A multipart/mixed gets a text/plain footer part appended after its children. Everything else (alternative, signed, encrypted, html, base64 text) is wrapped: mixed(<type>,text/plain). Output is a compact structure string.

Why this case matters

List managers that edit signed or encoded bodies in place break signatures and corrupt content.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
signed message	`"mixed(text/plain,application/pgp-signature,text/plain)"`	`"mixed(multipart/signed,text/plain)"`	Failed

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