I'd suggest that you don't open the emails Ray or if you do open them in plain text and no html.
Generally they load something or the other from the web and that tells the spammer that it is an active email address. It's ever so easy to do.
Not sure if all email packages can be set like mine is. It's set in plain text. Many read fine like that. If it's an html email I have the option to display it in that format without loading external references. Then if I want I can click again to load those as well. I may do if it's from say a tooling company that sends me offers every now and again – just to let them know I have read it for if they check this way.
This set up has other advantages as well – those infuriating bank, paypal and what ever they think of next ones. These do generally check for active email addresses and the daft links to sign in are more obvious.
One of the interesting aspects of Yahoo's email service is no html. Plain or rich text only. The above in part is why.
John
–