Sending an email with SWF was not the intention, but you could easily host your SWF anywhere and give a URL and they could play your game, most of the time cros

Sending an email with SWF was not the intention, but you could easily host your SWF anywhere and give a URL and they could play your game, most of the time cross platform except those few years where they weren't updating the linux SWF player to the latest version (which got fixed again later). If you can't host it yourself, you could put it on websites like newgrounds.