Audio file size reduction

I'm working on a project for someone that involves MP3 audio files (320kbps audio quality) and the only way I have to transfer then is through email. Each file is about 100-200 MB in size and I am wondering if there is a way to compress or somehow make the audio files smaller. I have tried 7-Zip and it does not compress much if any (the only compression I think comes from the text in the folder). Most of the reading I've done always involves reducing the MP3 quality, something which I would rather not do.



Is there a way I can either compress or package these files up and send them without reducing the audio quality?