[Dovecot] help on writing a rule for perventing spam

[Giuliano Gavazzi]

On T 22 Jan, 2009, at 11:49 , Charles Marcus wrote:

> On 1/21/2009, Giuliano Gavazzi (dev+lists at humph.com) wrote:
>>> The postfix backscatter readme is a good start, esppecially is you  
>>> are
>>> using postfix - and if you aren't, why aren't you? ;) ... but the
>>> concepts can be applied to any MTA...
>
>> I don't use postfix, because I use exim...
>
> And as I said... the CONCEPTS can be applied to ANY MTA...


well, first of all backscatter is not really the issue of this thread.
Secondly the concepts are not all that good. In particular the one  
entitled:

Blocking backscatter mail with forged sender information

that states:

"Like many people I still have a few email addresses in domains that I  
used in the past. Mail for those addresses is forwarded to my current  
address. Most of the backscatter mail that I get claims to be sent  
from these addresses. Such mail is obviously forged and is very easy  
to stop."
 From what I understand he is rejecting backscatter that is sent to  
some of his old addresses (with an identical forged sender, but this  
is irrelevant) and from there forwarded to his mail server. Very bad.  
If you have configured forwarding somewhere you must be prepared to  
accept anything from there, or else you will be the cause of  
backscatter as the peer server is a genuine server and not a spambot.
The old Postel rule Be conservative with what you send and liberal  
with what you receive (or something on those lines) might be too  
liberal in the current internet, but certainly should not be relaxed  
on the conservative part... The first thing an administrator should  
look for is to avoid generating spam of any sort, then he can think of  
ways to stop it (and even more responsibly to place a further burden  
on spammers with delays and the like, but this is something you can  
only do on an MTA).
Giuliano