[Greylist-users] Does Greylisting *always* work?

[martin dempsey]

Greylisting works great. I personally haven't had spamassasin flag a single 
message since I enhanced exim to do greylisting (I'm sure that won't last). 
On the other hand, I'm not sure of the collateral damage. Theoretically, 
since greylisting only tempfails a message, real messages should be retried 
and all real messages should eventually get through. I'm not sure the real 
world of real (sometimes broken) email programs works that way.

I already found one site where they were running sendmail out of inetd and 
*NEVER* processing the queue. The internet is apparently reliable enough so 
that 99% of their messages worked on the first try and they never noticed the 
problem. I knew their message was real - but it never got retried. So I 
looked into it and found they had the queue from hell going back years and 
never notices that a small percentage of their messages were not getting 
through. This isn't a greylist problem per se, but without manual research 
(and fixing it for them), I would have never received an email from them 
again.

It also appears that yahoo groups doesn't retry messages and that each 
message has a unique generated "sender email address". Looks like it might be 
a problem.

I also may be having a problem with a big ISP who is using a Mirapoint server 
that doesn't seem to be retrying most (but not all) messages . It identifies 
itself as " ESMTP Mirapoint 1.1.0". I've had users get "couldn't get mail 
through in 4 hrs messages, no action needed" messages back from the Mirapoint 
server even though it appears Mirapoint only attempted message delivery once.

Evan: In your document you state based on 346k triplets more than 97.4% 
effectiveness at bouncing spam. That was assuming all email was spam. It also 
apparently assumes all messages that didn't get though were spam. Do you have 
any idea of the number of messages incorrectly blocked that weren't spam but 
didn't get through the greylist due to people using broken/stupid MTAs or 
other problems?