Programs which send out mass mailings can determine if an email address is worth their resources to send unsolicited email to, based on custom variables.

For the consumer, those that run spam filters, frequently unsubscribe from emails and never go to the sites promoted in the emails will be less likely to get mailed, and those that are bad about getting rid of spam, or frequently purchase from spam will get more email. It allows for targeted mailings for the spammer, and less email for those that are zealous in keeping their inbox pure.

The benefit for the spammer is for the usage of fewer resourced.

The benefit for the person hosting this site is that every time someone verifies an address, it adds it to their database. They can then sell lists of email addresses without having to harvest them. Email addresses with better statistics can be sold for more.

The benefit for the end user is that if they are successful in avoiding spam, they won't get spam from those spammers using this program to verify addresses.

I will be posting the mySQL table format soon.