[Xylakant]

you can use encrypted mail, however that requires you to convince all people that you exchange mails with to use encrypted mail as well.

You could use a hosted email service in another country where the american authorities don't have easy access. Europe might be an option. However, as with hosting your own email server, that's only a partial solution: If you communicate with other people, your mail is not only stored in your inbox but also in their outbox. So they'd have to use a mail provider outside the US as well - see the first paragraph.

The best is probably a hybrid solution: Try to educate as many people to use encrypted mail as you can and use a mail server that's located outside the US. It doesn't provide 100% protection, but at least you're not part of the dragnet search.

[olefoo]

Errr... the NSA is specifically charged with monitoring communications that cross US national borders.

Using a mailserver in a foreign jurisdiction makes it more open to legal interception by the US government; not less.

[Xylakant]

Valid point. It's a different branch and a different issue though. Mails that are already on your server and stored there would be relatively safe. Make sure communication is encrypted.