If you want to do that, you have 2 choices. You can get a speaker switcher that switches between your studio monitors and PC speakers, if its external speakers and not laptop speakers. note you will still need to turn your audio interface on. I use the Coleman SPK5+1 switchwer. Its great, i can switch between 5 different pairs of speakers and a sub.
if you want to use your PC's built in sound card, then you need to enable it and disable your audio interface
No, speaker choice has nothing to do with sending project via email.
To send music files, i use hightail.com. i can send up to 2 gigs for a small yearly fee. As far as you posting music to a forum for people to hear, you need to publish it and provide links to it, like soundcloud..