This module turns dominique@dominiquedecooman.com [4] into
<a href="mailto:dominique@dominiquedecooman.com">
The code in the module can be found on http://drupal.org/node/151638 [5]
I just put it in a little module ready to be downloaded and installed.
Installation : Just put the module in your sites/all/modules folder, install the module and turn the filter on for the right Input format in admin/settings/filters
EDIT: Or you can just use the spamspan module http://drupal.org/project/spamspan [6]
Links
[1] https://dominiquedecooman.com/blog-topics/email
[2] https://dominiquedecooman.com/blog-topics/spam
[3] https://dominiquedecooman.com/sites/default/files/emailob.rar
[4] mailto:dominique@dominiquedecooman.com
[5] http://drupal.org/node/151638
[6] http://drupal.org/project/spamspan