Fighting SPAM with a Postfix relay server

2009-07-16 Thread Antonio Navarro Navarro 
Hi all!

 

I have configured a Postfix server with amavisd and spammassassin as relay
server for several domains. All the mails sent to @example1.com and
@example2.com are received in the postfix server, and then redirected to the
real mail server for this domains.

 

We are receiving thousands of SPAM mails with headers similar to this ones:

 

From: randomt...@example1.com

To: realu...@example1.com

 

As this relay server only works receiving mails from external servers (all
the internal communications are handled by the real mail server for the
domains), is impossible to receive a real mail message with From: And To: in
the same domain.

 

How can I avoid this? I don’t want the postfix relay server to accept mails
with a from address in (@example1.com OR @example2.com) AND (to address in
@example1.com OR @example2.com).

 

Best regards,


 http://www.ticsconsulting.es/ 




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Re: Fighting SPAM with a Postfix relay server

2009-07-16 Thread Noel Jones 

Antonio Navarro Navarro wrote:

Hi all!

 

I have configured a Postfix server with amavisd and spammassassin as 
relay server for several domains. All the mails sent to @example1.com 
and @example2.com are received in the postfix server, and then 
redirected to the real mail server for this domains.


 


We are receiving thousands of SPAM mails with headers similar to this ones:

 


From: randomt...@example1.com mailto:randomt...@example1.com

To: realu...@example1.com mailto:realu...@example1.com

 

As this relay server only works receiving mails from external servers 
(all the internal communications are handled by the real mail server for 
the domains), is impossible to receive a real mail message with From: 
And To: in the same domain.


 

How can I avoid this? I don’t want the postfix relay server to accept 
mails with a from address in (@example1.com OR @example2.com) AND (to 
address in @example1.com OR @example2.com).


Using reject_rbl_client zen.spamhaus.org will likely get rid 
of the majority of these.


Postfix can't reject based on multiple header comparison; you 
need a content_filter such as SpamAssassin for that.


Postfix can reject an envelope sender in your own domain 
that's not from mynetworks or sasl authenticated.  See the 
archives if you need an example.


  -- Noel Jones

Re: Fighting SPAM with a Postfix relay server

2009-07-16 Thread Anthony Wong 
The postfix add-on software smtpprox can do exactly what you want, with a
little modification.  Since smtpprox is written in perl it can adversely
affect system load, but it works very well for us and the affect on our
system load is negligible.