Milter-greylist

Emmanuel Dreyfus wrote:
> On Thu, Oct 27, 2005 at 10:50:23AM -0400, Matt Kettler wrote:
> 
>>That is true, you CAN do that. But that's not where milter-greylist ties in.
>>Milter-greylist has made the deliberate choice of greylisting before the STMP
>>DATA phase in order to save bandwidth.
> 
> 
> IMO it was more to have greylisting activated on a per recipient basis.
> 

Fair enough. I hadn't even considered that angle when I wrote my response.

That said, it would be a considerable waste of bandwidth to wait until after the
DATA phase given that the accuracy boosts you would see from it would be very
small percentage wise.

In my experience, 94.4% of spammers never retry or resend at all. So your
absolute best-case gain would be to pick up the last 5.6%. However, I doubt
you'd get more than 1% additional elimination this way. Most of that 5.6%
appears to be abused relays that really do queue, and no greylist will ever
eliminate those sources, just delay them so you can get better RBL hits.

The network bandwidth overhead of greylisting pre-data phase is pretty small.
Maybe 200 bytes, at most? However, the post-data phase overhead could be large..
say an email with a large .zip attachment.. 100MB?

So, even if you could still do per-recipient filtering after the DATA phase, it
would still be a bad idea.