Don't allow the email address to be viewable in the source code.
i.e.
<a href="mailto:me@you.com">email me</a>
Do something like:
<?php
if($_GET['emailme']){
if(mail('me@you.com', 'Subject', 'Message', 'FROM:website@domain.com\r\n'))
echo 'Thanks';
else
echo 'Error';
} else {
echo '<a href="mailme.php?emailme=1">email me</a>';
}
?>