There can't be that many (edit - that many Email spam startups at least. Web spam, blog spam etc are another issue). It's a crowded and relatively mature market

There can't be that many (edit - that many Email spam startups at least. Web spam, blog spam etc are another issue). It's a crowded and relatively mature market that just went through a round of acquisitions of mature private anti-spam companies (CipherTrust, IronPort and Postini)