"They" do it all the time

They being spammers. You don't actually think those are legitimate email addresses they use? I'm postmaster on a couple of domains and I get bounces to nonexistent email addresses (from equally nonexistent email addresses that the spammers seem to have gotten from somewhere). Come on. telnet to port 25 and go from there. There are so many open relays still out there. Or set up your own smtp server. Something like 80% of the bots I've looked at have one.