Using a captcha can help prevent spam. One of the best solutions out there is the Google ReCaptcha – it’s free and not too intrusive during form submission.
A significant number of your users can now attest they are human without having to solve a CAPTCHA. Instead with just a single click they’ll confirm they are not a robot.
WP Job Manager, Applications, and Resume Manager have ReCAPTCHA settings built in. See this page for details of how to get a ReCAPTCHA key and enter your settings. Thats all there is to it!