How to Stop Spammers using Form without Adding Captcha?

A client's webpage with contact information is receiving spam mail from a spambot. How do I stop this from happening without adding Captcha? As listed above, I tried using some css codes but it hasn't worked. 

Hi,

I believe using CSS codes won't worked in preventing spammers using your form. What is standard and is usually used by most websites are adding Captcha codes or human verification inputs (these includes like adding a custom code that you and the user only knows, kinda like a coupon code).

Here are other ways that you can use:

1. Adding limitations to your form, http://www.jotform.com/help/137-How-to-Limit-Submissions-in-a-Form.

2. Get the IP address of the spam submission and if your web hosting site has the feature to block it, you can add the IP address of the spammer there. Here's the tutorial on how to get the IP address, http://www.jotform.com/help/31-How-to-See-IP-Addresses-of-Form-Submitters. 

3. Other captcha widgets that we have, http://widgets.jotform.com/search/captcha.

I hope this helps.

Thank you.