Some job sites are notorious for 'harvesting' - advertising jobs in order to collect the personal details of job-seekers, which are then sold on en masse to third parties (often to marketing companies, but sometimes to unscrupulous outfits who will use the information to steal your identity). I have come across one or two such sites recently, and whenever I find one I go to WOT and SiteAdvisor and post a site review there to let others know what to expect.
To block incoming mail from reaching your PC you can use McAfee Security Center. This has, under 'Web and Email Protection' a section for Anti-Spam - some of those settings can be adjusted to filter out those annoying emails.
If you have a major problem with spam from agencies, try setting the Spam Protection Level to Aggressive, and then block individual senders by using 'Custom Filtering Rules' (see below); or - if things are really bad - set the Spam Protection Level to Restricted, which rejects everything that isn't specifically allowed. Of course, then you have to add each sender that you want to be able to mail you into the 'Friends List', which could get tedious (you'll miss out on a lot of mail that way).