a good idea for spam

I use Fastmail as my email client because it allows me to check all of my many email addresses in one place (including my rusty old practicalhippie Hotmail account) and it's accessible via the web (so I don't have to be on my computer, which is great for travelling around.)

It also includes a great feature I haven't seen elsewhere: the ability to make it look like your email address is bouncing and therefore invalid. It's the electronic equivalent of "return to sender, no such number." This doesn't stop spam, however it prevents people who sell lists of "valid" email addresses to other spammers from including me in their lists.

Their spam filtering works pretty good too :)