{"success":true,"data":{"id":"attachment-no-filename","label":"Attachment has no filename — malformed bulk mailer or deliberate content-scanner evasion","description":"An attachment arrived with an empty or whitespace-only filename. Standard MUAs (Outlook, Gmail, Apple Mail, Thunderbird, and the major bulk-mailer ESPs) always assign a filename to every attached part — the Content-Disposition header carries a `filename=\"...\"` parameter even for anonymous parts. An attachment with no filename means either (1) a malformed bulk mailer that skipped the header (rare but legitimate edge), or (2) a deliberate evasion technique: some malware tooling omits the filename so content scanners that rely on filename-extension matching for threat detection (exe / double-extension / archive checks) have no signal to work with. Weighted at +2 — low because the legitimate malformed-bulk case exists, but it pairs well with other attachment signals: an unnamed attachment with a suspicious MIME type or mismatched extension stacks above the delete threshold.","tier":"warning","category":"attachment","isThin":false}}