What if you’re downloading a product demo, need a unique address to get the key, and never want to hear from that company again? Good luck! Actually, you don’t need good luck, just mailinator.
Send to any address at mailinator.com (or one of several other domains) and then go to the site and check your email. But make it a long, complex address, because there’s no password. In fact, anyone can check “your” email if they know the email address (including the person/company who sends email to you).
If you completely understand the limitations, this is a wonderful service.