Help can I stop people spamming email addresses

I am a newbie to this and am struggling. I have a clasifieds site and am concerned about people spaming the peoples email addresses as the are displayed on the pages on my site. Is there a way that if someone wanted to reply to an advert that a form could appear and this allow them to key the reply, this would then query the database and send an email with out the email addressbeing seen? I have the database (mysql) called carsale in that I have a table called owner, with a unique id and row 13 is the email field. I managed to call up the correct unique id but cannot get the mailpage to send. Sorry to be a pain I am trying to learn this language. Any help gratefully received Iain