File type rules were created to allow administrators to control large personal content, such as music or video files. The Thru server cannot block certain file types at upload time (files can be part of folder uploads which cause exception handling issues). If you need to create a policy to prohibit music files, mp3 for example, you can create a fixed period or inactivity definition with zero days and create a file type rule on mp3 extension. Such a rule will delete mp3 files on every cycle.
There might be cases where business-related mp3 files need to be uploaded. To allow that, Thru server allows excluding file type rule enforcement on selected folders. The exclusion is always for all file type rules and for all for all subfolders. Exclusive user rules and file rules always hide file-type rules. The following diagram summarizes file-type rules behavior: