The mod_case module is designed to help ProFTPD be case-insensitive, for those
sites that may need it (e.g. those that are migrating from a Windows
environment or have mounted Windows filesystems).

mod_case works by performing two checks on the filename used in FTP commands.
First, mod_case will scan the directory to see if there is already a file whose
name exactly matches the given filename. If not, mod_case will scan the
directory again, this time looking for case-insensitive matches.