Am Dienstag, 23. September 2008 schrieb mir Alex Efros:
> Sorry for OT, but I wanna install spam-protection tool based on
> confirmation email request (somebody send me email, my tool delay that
> email and automatically reply requesting confirmation, he confirm, my
> tool receive that confirmation and: 1) add his email to while-list; 2)
> deliver his initial email to my mailbox). 

Assume both partys use this mechanism. It's pretty funny, every party 
waits for confirmation and waits for confirmation of the confirmation 
request and waits for the confirmation of the confirmation of the 
confirmation request ...

And I don't want to confirm you anything, what a spam robot couldn't do, 
too.

You could make a whitelist in your spam filter if you know your opposite.

Regards
Oli