Attachment .pdf.cab and it should be captured as bad attachment but did not

I have noticed that some mails did not pass spam assessment and
check trough protector. It is on spam list but not detected this happens only on several mails per
day, rest of them successfully is assessed by protector antispam filter.

It is because the mail size is above the Max size configured for spam checks.

The parameter is in menu Anti Spam - Setup. Try increasing it to 1600 and resend the mail.