Why don't you use email encryption?
mixmax: I actually tried a few years ago since I routinely sent patent applications, business plans and other sensitive information in e-mails. Unfortunately I couldn't get anyone to install encryption software at the other end (PGP) so I had to give up. Not even our patent attorney seemed to think that it was worthwhile to encrypt his mail.I could probably have gotten a lot of really good patents by sniffing his mail and sending in applications before his customers got around to it :-)