You can use regular expressions for that.

Please see http://www.regular-expressions.info/email.html and http://www.php.net/preg_match

:)

--[Edit]--
Sorry, I didn't read all the way through. If you don't like the required email format trick above, then it looks like you want a form of "CAPTCHA". Here's a nice tutorial for that :)

http://www.white-hat-web-design.co.uk/a...