Viral mailers are are usually free to join sites where you read other members emails in exchange for them reading your own. You will receive emails from other members of the site you have joined and you can earn mailing credits by clicking on the link in the email. This link will open up a new window with the promoted business opportunity. You will earn the mailing credits when you have viewed the site for the designated period of time and the click on the matching icon, this will then ensure that Mailing Credits are assigned to your account. These credits are then used for sending out your own email ads or converting them into banner and or text impressions.
There are a myriad of Viral Mailers on the Internet and it can be sometimes hard to know which ones will work for you and which ones do not.