If I simply copy sa-learn from box1 to box2, can the users run it without having to install the entire SA package on box2?
No. sa-learn requires most of the full SA package to run.
Sa-learn is mostly just a perl-script wrapper that winds up instantiating a SA perl object and calling it. It's not a stand-alone binary file, and cannot run without the rest of the SA install, or at least the perl libraries part.
You don't need the copy of SA on box2 to actually be involved in scanning mail, but you at least need the full install of the perl code.
