[ILUG] using postgrey as a cheap way to initially avoid lots of spam

[Niall O Broin]

On 13 Dec 2006, at 23:36, Brendan Kehoe wrote:

> I just set up the postgrey package as described at
>
>   http://www.debuntu.org/postfix-and-postgrey-a-proactive-approach- 
> to-spam-filtering
>
> It's already saved a lot of CPU time on zen.org as it doesn't waste  
> its time analyzing as much crap.  Pretty cool.  It just sends an  
> SMTP message back asking for the message to be resent later, which  
> reportedly isn't heeded by most spam distribution software.  At any  
> rate, it seems to be working pretty well for me so far. :)
>
> I found some debate about the risks of SMTP 450 errors causing mail  
> to be discarded, but from what I can tell most major mail server  
> apps just postpone delivery.

You're a bit late to the party Brendan :-) Many denizens of this  
parish have been using greylisting for some time now, and indeed, the  
parish priest even does so (Colm, on morrigan, for the ILUG list, in  
case my analogies are getting out of hand).  However, there are LOTS  
of mail servers out there which are not RFC compliant and will barf  
when faced with greylisting, and there are also big systems which  
will retry with a server from a netblock which is so different from  
the original that greylisting regards it as a new IP.


Michele Neylon of Blacknight has a list of Irish ISPs which he adds  
to his whitelist. I don't think they're all non RFC compliant, but  
his attitude is I believe that for Irish users, whitelisting the  
major Irish ISPs is a good idea, and suppose he's not far wrong. I  
thought Michele had given me this list before, but if he did, I don't  
seem to have implemented it, so perhaps he could post a pointer to it  
here as a public service.


Niall