Michael Heydon wrote: > Exim wrote: > >> I just had a client ask for something I haven't done. He wants emails from >> unknown users to be sent back with a "are you human" request they must >> respond to correctly. If they do, then they will be automatically added to >> a list of valid senders. >> >> > > I believe it is called challenge response filtering and it is the most > horrible antispam tactic I have seen. If you really absolutely can not > get out of doing it, please make sure that you do it as a last resort, > check SPF, run SA, use DNSBLs. > >
Not only that, but two people, each using CR, will never get to talk to each other; rather they will fire away their "are you human" messages at each other. It only works if a tiny minority of people use it. And, if you do use it, you will likely never hear from a large number of people. I won't respond to them; many of those messages get caught in real spam filters. So all in all, it's a really bad idea. Google for challenge-response. You will get a good variety of ideas. -- o__ ,>/'_ o__ (_)\(_) ,>/'_ o__ A day may come (_)\(_) ,>/'_ o__ when the courage of men fails, (_)\(_) ,>/'_ when we forsake our friends and break all (_)\(_) bonds of fellowship, but it is not this day. It is not this day! This day we ride! -- ## List details at http://lists.exim.org/mailman/listinfo/exim-users ## Exim details at http://www.exim.org/ ## Please use the Wiki with this list - http://wiki.exim.org/
