Adult Opt-in Emails for sale
 

Does anyone know what the going rate for Opt-In emails for general porn? How about by niche?

I see companies paying webmasters $1 for each email they collect, but what is the average lifetime residual value of email? Any big company knows this and thats how they figure out how they can afford to pay $30 a sign up.

I collect opt-in emails but I never ran a campaign so I cant come up with a lifetime value figure per email. Thanks