If you will be publicly displaying email addresses on your website, you should make sure they’re encrypted to keep them from being harvested by spambots. You can download and install the Invisimail module to use as a filter for your input formats; this will encode any email addresses within the body of a filtered text field.
If you have dedicated email fields, then you should download the CCK field type Email Field. You can use Email field together with Invisimail to protect any email addresses displayed on your site. To turn Invisimail on for a CCK email field, just go to the “Display fields” tab for the content type and enable it there.