Using mailto form is not any way spam protected. It i just like giving your e-mail directly to spammers. There are some solutions on the Internet that can help:
40 Secs Contact Form - Website Contact Form generator, simplest to install
It's a php script generator. You don't need to be a programmer to install it. Very easy and effective. And spam protected.
And my favorite is
Free Contact Form generator and anti-spam protector - WRASAP (Will Reply As Soon As Possible)
It's free and looks very similar to the previous one. Just like your personal web contact from with spam protection.