Topic: spam challenge and response

[Mark]

Is there a contribution or way to set up a challenge and response system in the mail server?

A friend of mine is blocking spam this way: When mail from an unknown address is recieved the mail server replies with a lengthy message specifying a method to request authentication from the recipient. Challenges that bounce are sent to the bit bucket; challenges that are resubmitted correctly are admitted.

I am told this has reduced spam by a considerable percentage. Anyone have an opinion?

 - Mark

[nate]

I believe what you are describing here is known as 'gray listing', …and yes, it is the way to go!  
 
Lets get the e-smith ‘smiths’ on this one, …all you genius, selfless, wonderful people that do these things, and someone to come up with a “how-to” on it, …or maybe even a server manager panel eh?
 
(wish-list item)

[Nathan Fowler]

TMDA  (Tagged Message Delivery Agent) http://tmda.net/

It's already invented, and can be optionally implemented in SME.  Search the forum

[nate]

Okay first,

I admit to ignorance, but I believe that TMDA sends back a message that must be replied to by a ‘human’ before it will get through.  And, after re-reading Mark’s posting this is probably what he IS talking about and looking for.  However, I have heard that it is possible to configure a mail server send back what is essentially a “busy signal” that tells the ‘server sending the message’ to “try again in a little while”, and this is enough to substantially reduce spam without causing any inconvenience to “real” first time senders.
 
.nate

[nate]

THIS IS THE THING:
 
http://projects.puremagic.com/greylisting/

[Mark]

Thanks, Nathan, for the link to TDMA. That does look like a good solution.

Thanks, Nate, for the link to grey listing. That is a very interesting solution as well.

 - Mark

[Doug M.]

Just thought I'd through in that you may want to look into spammassassin as well. I had considered TMDA once but after getting a few responces from similar systems to my emails I realized I didn't want to harrass my aquantances similarly. Search spamassassin at http://contribs.org. My two cents to spend on what you'd like....