Spam is a big area and we are investing heavily in trying to solve this problem. I would love to hear your point of view about why you would not want to use this method. We are open to suggestions.
While I think its great that you guys are attempting to do something about spam, I don't think that "authentication" emails are the way to do it. First off, as "ef" pointed out, the authentication email that is sent back to the original sender is seen as spam by different email clients. If someone doesn't check their spam folder (or if it's deleted) then they will never see the authentication email.
Maybe this is just a personal thing with me, but I view authentication emails the same as return receipts. Very annoying. When someone sends me a return receipt, I never acknowledge it. It's as if the person doesn't trust me to respond, so they want the verification that I read it.
Another thing, say I purchase some software off the internet. I am then sent the registration information but an authentication email is sent back to the purchase site. How can I be sure the place I made the purchase will get the authentication email and respond? In many cases, the process is automated and they won't respond to the authentication request, so I'll never get the registration info.
Using the authentication method may help reduce spam, but it will also kill valid emails. I don't know the answer to spammers. Maybe seek them out, arrest them, throw them in jail for life, feed them to lions, etc. I don't know.
Good luck with whatever methods you can come up with, but as I stated before, I won't use the "authentication method" and neither will many others.
Author