Attachment filters are used to manage exceptions for file attachment checks. Files that match an "allow" rule skip content checks including QuickSand. Files that match a "deny" rule are always blocked.
Rules can be set for recipient/sender email address or domain.
NOTE: even if the list is empty, a bug list of file extensions and file types are blocked by default, check out the list.
All the common vectors of email threats are blocked by default, you need to enter an "allow" rule to let them through.