The answer is simple. There are computer programs out crawling the Web collecting email addresses for spam mail lists. For this reason, I never post my email address on the web and encourage you to do the same. I initially had an image of my email address on my webpage which the spiders cannot read, but I found people who put links on their pages to me and then copied my email address out of the image and into their page. So, this is the result of my personal war against spam.
Vigilance is the price of bandwidth.