{"success":true,"data":{"id":"malformed-message-id-header","label":"Malformed Message-ID header (RFC 5322 violation)","description":"RFC 5322 §3.6.4 requires Message-ID headers to follow the format <local-part@domain>. Every legitimate MTA (Gmail, Outlook, SendGrid, Mailchimp) produces a well-formed ID. Fires when: (1) Message-ID contains non-ASCII characters, (2) Message-ID exceeds 255 characters, (3) Message-ID is missing the required angle-bracket+at-sign RFC structure, or (4) both Message-ID and In-Reply-To are absent (orphaned email with no provenance). Score: +2 trash.","tier":"danger","category":"header","isThin":false}}