Advantages: Potential of increasing a spammers cost of sending spam.
Limitations: It is possible that the spammer will think the hits are legitimate and if the spammer has user level tracking in the links it could make the spammer think he has a person interested in their spam message which could ultimately lead to more spam messages.
How does it work: Punish loads the web pages in a spam email message a certain number of times. Since nothing is being bought from these visits it could minimally increase the bandwidth costs to the spammer without any increase in revenue.
Recommendations: We don't recommend using punish at this time for most users. It can be minimally effective at increasing costs to spammers but generally this is not worth the time it takes to punish a message.