Well, at least not in the past several years.

I have read several posts on AR about SPAM, and I always wonder why the "challenge / response" system is never discussed.  It seems many people are missing the boat when it comes to SPAM elimination. 

Filters don't work, period.  As soon as you figure out a way to filter your email, three things will happen:

1.  You won't get any "Viagra" jokes from your friends anymore.

2.  You will undoubtedly miss an important email from a client, because they used some word or phrase that your filter misinterprets as spam, possibly blowing a commission.

3.  The spammers will figure out a way around the filter.  High security usually filters out the good guys.  The bad guys work around security.

Here is how it works:

All of your email is currently downloaded from whatever server accepts your mail.  For example, my server is AZWM.

With the challenge / response system, there is a go-between.  In other words, the SPAM goes to the go-between server first, then is downloaded to your computer.

When the go-between server gets your email, it checks it against a database of everyone who has ever sent you email.  If the server recognizes your Aunt Betty's email address, it just sends the email along to you.  Easy peasy.

If it's an email from a stranger, this is when the "challenge" part comes in.

The server automatically sends an email to the spammer, asking the spammer to identify themselves.  95% of the time, the email is "bounced back" because spammers almost always use fake email addresses.

If the email is bounced back, it is spam, and I never see it.

If the email contains a virus, it is deleted and I never see it.

If the email is from a human being, they usually just click the "verify" link.

There is only one tiny flaw in the system:  Sometimes people are afraid to click the verify link.  That's perfectly okay, because I skim through the spam folder every couple of days just to make sure I am not missing anything due to paranoia.

Also, you can add "new senders" anytime you want, and they won't get the challenge.  For example, everytime I email somebody new, I add them to my safe list, so they don't even know about my spam thing.

You can Google "spam challenge response", or just go with the service I use:  SpamArrest.  It's worth every penny at about $48 per year.  I haven't had a virus or the threat of a virus since I began using it.