First off, read
this.
Secondly, mIRC isn't filtered. mIRC is just a program for connecting to an IRC network. There's nothing in the mIRC program to filter anything that you receive, pertaining to filesharing or anything else. The particular IRC network you connect to could potentially have some kind of server-side filtering, however I'm unaware of any network doing such a thing.
Regardless of filtering and mIRC's intended use, the DCC file protocol is
very very poor as a full-scale file transfer protocol, and IRC is a
very very poor medium upon which to carry out even the most basic filesharing operations (finding files, etc.). If you want to share files use a better protocol, for everyone's sake.