Symphony.

Is there any built in functionality to encode email address? If not i think that would be a really valuable extension. Expression Engine has this functionally and it is currently one of my biggest grips about Symphony (other then that I love it!).

http://expressionengine.com/docs/templates/globals/singlevariables.html#varencode

You can always use javascript to achieve this. One the websites I build I use a combination of CSS and javascript to build my e-mail links.

Of course I also just use a PHP contact form.

Why do so many people encode their e-mail addresses? Can't spammers easily program the robots to crawl for entity combinations that represent an e-mail?

To some degree, yes. Right now I use this method:

<script type="text/javascript">
    <!--
    var name = "name";
    var domain = "website.com";
    document.write('<a href=\"mailto:' + name + '@' + domain + '\">');
    document.write(name + '@' + domain + '</a>');
    // -->
</script>

Because the URL is so mixed up in the code, not to mention the commenting, it makes it much more difficult for a spider to read my e-mail address. You could even compress this to make it more complicated.

markdown formatting extention offers email encoding out of the box

yes, but we prefer textile and the client has some experience with textile. It would be nice if there was a plugin that took the email address as a variable and returned it encoded.