Try one of these:

www.hushmail.com

www.cryptomail.org

http://cvs.sourceforge.net/viewcvs.py/*checkout*/invisibleip/contrib/htmldoc/en/index.html?rev=HEAD#chapter7

Don't forget Xmail (https://www.xmail.net/index.php)! That last link doesn't load for me. Anyone else having this problem?