There are better ways than using email, that’s for sure. You can find a nice review of various collaborative writing tools on LaTeX wikibook: SpanDeX and ShareLaTeX allow for only one collaborator per project within their “free” licenses. WriteLaTeX is like EtherPad for LaTeX, anyone who has a link to the document can participate in editing. Unfortunately, it lacks advanced functionality such as version control and cloud support. Very promising project SciGit has not been launched yet.
Online collaborative writing of LaTeX documents