The current file transfer settings on openfire server configuration allows diabling file transfers to remote servers. How do I turn off file transfers to local networks also?
take a look at the documents within “Community Plugins” as there are some blocking plugins, you may find there something useful.
Blocking file transfers is not possible as they are normally P2P. The best way to prevent file transfers in a company or school is to forbid it in a legal way (so not technically). There is some security-through-obscurity solutions to block file transfers though, but this can be easily by-passed and I would not recommend it at all.