This article has a nice summary of why/when/how to use a “dummy” email address to avoid eternal spam when a site insists you enter an email address. I’m partial to Mailinator myself – all you need to do is enter and then go over to the site and enter it to see any incoming email. Of course, the rest of the world can see your mail too, and it disappears after a few hours. I have noticed that a few sites have rejected the domain, so I may have to try out the Email on Deck app if that happens again.