[Techtalk] re: Postfix reload

[Carla Schroder]

On Monday 15 September 2003 11:47 pm, showercurtain wrote:
> This is the bit I'm confused about. When postfix is configured to
> block certain traffic, what exactly happens to that traffic, where
> does it go? If some email to our organisation is blocked by the RBL,
> does the sender automatically receive a bounce message? 

OK, let's make sure of our terminology- Spamassassin is not a RBL, it's a 
filter. You know that. :) So yes, sending bounce messages from Spamassassin 
is a waste of time, because it does not have the ability to get past forged 
return addresses. 

RBLs are different, because they block IP ranges at the DNS level, they don't 
care about forged mail headers. It is considered a good practice to send an 
explicit 554 reject message, in case a legitimate message is blocked, then 
the sender knows what to do. The sender gets something that looks like this:

554 Service unavailable; [204.71.191.177] blocked using 
spews.relays.osirusoft.com, reason: [1] listbuilder, see 
http://spews.org/ask.cgi?S770

Postfix has a great default configuration, you shouldn't need to change 
anything.

 Here are two good resources:

http://www.postfix.org/uce.html#default_rbl_reply
http://jimsun.linxnet.com/misc/postfix-anti-UCE.txt

The second one is great, one of the best documents on configuring Postfix to 
use RBLs and block spam that I've seen. Don't forget the Security Focus 
series I mentioned earlier.

I hope that helps!

--
~~~~~~~~~~~~~~~~~~~~~~~~~
Carla Schroder
www.tuxcomputing.com
this message brought to you
by Libranet 2.8 and Kmail
~~~~~~~~~~~~~~~~~~~~~~~~~