"LISTSERV site administrators' forum" <[log in to unmask]> 
wrote on 09/13/2006 04:35:26 PM:

> Or you might use a service that asks for the sender to confirm their 
email
> authenticity by clicking on a link and adding them to your whitelist. 
> Since the message specifically asks the user to click a link (http) 
there is
> no valid (or another /dev/null) return email adr catching any loops or 
error
> messages.   I ran across this service some time ago but misplaced the 
link
> so if someone else knows what im talking about PLEASE send links on
> company/applications that does this. 

I really hate those sites.  Think about it...  You're handing over your 
email address to some third party.  Do you trust the privacy policy on 
them?  How do you know that they aren't just a front to gather email 
addresses to spam?  Do you want to force your subscribers to agree to some 
third party's rules?

If presented with one of those, I decline to participate in their 
stupidity.  Do you really want to put a barrier in front of your users?