Even that wouldn't help if your server is hosted in the US. If they really want access to your e-mail, they can just have your hosting provider give them access

Even that wouldn't help if your server is hosted in the US. If they really want access to your e-mail, they can just have your hosting provider give them access (or get the data for them), and under the Patriot act, they can't even tell you about it. Another other solution would be to use e-mail providers (or hosting solutions) outside of the country. Vancouver, Montreal, and Toronto, for example, have excellent connection to the US fibre networks (my company has its own pipe from Level 3 from Seattle to Vancouver). Host a server there, and no amount of government intervention is going to get your data, and hosting companies here (well, the good ones) won't give your data up without a subpoena or a warrant (and are able to tell you).