Unsolicited email 2. In the case of Search Engines, that is how some of them find and index new sites. The problem is that some of those robots grab email addresses from websites, email signatures and usenet posts. They then add those addresses to spam lists, which they can use, or sell to other spammers.
Email addresses are easy to find, free for the taking.
Don't put your email address on your website, or in Usenet posts. Modify the email address on your site - you won't get nearly as much garbage email. The problem with this method is that some folks don't understand it, so you will miss out on some emails. Well, the robots aren't human, and can be tricked. This wastes the spammer's time and money, by sending mail that won' t be received.