Transparent email proxy

[Paul procacci]

Paul procacci wrote:
> Olivier Nicole wrote:
>> Hi,
>>
>> As an ISP, or the person in charge of a large organisation, have you
>> ever set-up a transparent email redirection: all outgoing email would
>> be proceeded to an outgoing server in order to check for virus, spam,
>> whatever.
>>
>> Best regards,
>>
>> Olivier
>> _______________________________________________
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>>   
> The answer to your question is yes.  To elaborate a bit more however 
> here is a personal document I wrote (i.e. wasn't intended for anyone 
> else), hopefully it provides you with good enough information and/or 
> the information you were looking for.  Mind you, this is BSD and qmail 
> (yes, I'm a fanboy) specific.  This assumes you are familiar with the 
> software I decided to use under the components heading.  Certainly 
> feel free to ask any questions.  I realize the document isn't 
> "production quality" due to the reasons given about, but rest assured 
> I can vouche for this method.
>
> Additionally note, this is obviously not the only method.....just that 
> it's my method.    ;P  Cheers!
>
> ~Paul
>
> ----------------------------------------------
>
> I have 5 machines behind a load balancer, one of which is FBSD 4.11, 
> and the other 4 are FBSD 6.2.  The component list I used is as follows:
>
> Components
>
> tcpserver
> daemontools
> qmail w/ QMAILQUEUE patch
> qmail-qfilter
> spamassassin
> *custom c scripts  (These are optional; one is provided)
>
>
> Flow
>
> This is the current flow of any emails that reach the cluster. Note 
> the items listed within *'s are custom programs and explained later in 
> this document:
>
> tcpserver->qmail-smtpd->qmail-qfilter->spamc->*reject_spam*->qmail-queue->qmail-remote 
>
>
> **Note :: reject_spam is included because that is needed for denying 
> emails.  (You could rewrite it in perl or sh if you needed to)
>
> Installation
>
> The installation for any new and existing proxy boxes is extremely 
> straightforward.
>
> For all but qmail listed above, use the ports tree.
>
> Setup spamd to create the /tmp/.spamd.sock socket.  That's what I call 
> mine, yours can/will vary.
>
> Once all this is installed, create /etc/tcp.smtp with the following 
> entry and build the cdb file:
> :+RELAYCLIENT=+QMAILQUEUE=/var/qmail/bin/qmail-queue-spam
>
> Ensure tcpserver uses that file(i.e. -x)
>
> While in /usr/ports/qmail.....
>
>  a) upload the attached files (patch-qmail.c and patch-Makefile) into 
> ./files/
>
>  b) edit patch-qmail.c to reflect a message you would like to give.
>    '+    case 20: return "DAnti-SPAM Threshold Reached see 
> http://domain.com/legal_information.aspx";'
>
>  c) type: make extract
>
>  d) type: make patch
>
>  e)  copy the attached file (reject-spam.c) to ./work/qmail*/
>
>  f) Now, I haven't included some of my patches here do to sensative 
> information.  Therefore, you'll need to edit the Makefile 
> (work/qmail-*/Makefile) to removed any and all references to 
> check_block and reject-record-spam.
>
>  g) type: make install
>
>  h) copy reject-spam to /var/qmail/bin
>
>   i) Copy the  attached shell script (qmail-queue-spam) to 
> /var/qmail/bin/; that is going to tie this together.
>
> Please note that it's NECESSARY to use the local software FW to allow 
> relaying.  IPFW is a good choice (my preference anyways).  Deny 
> everything to port 25, and  only allow the hosts you want.  I found 
> this to be the easiest.
>  Then on those hosts, smarthost the "hidden" (not really) machine.
> ------------------------------------------------------------------------
>
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My attached c file got stripped.  Here is it.

reject-spam.c
-------------------------------------------------------------------
#include "stralloc.h"
#include "substdio.h"
#include "readwrite.h"
#include "getln.h"
#include "str.h"

stralloc s = {0};
substdio i = {0};
substdio o = {0};

char ibuf[1024];
char obuf[1024];

int main(void){

        int match;

        substdio_fdbuf(&i,read,0,ibuf,sizeof(ibuf));
        substdio_fdbuf(&o,write,1,obuf,sizeof(obuf));

        for(;;){
                if(getln(&i,&s,&match,'\n') == -1) _exit(81);
                if(!match || s.len == 1) break;
                if(!str_diffn("X-Spam-Flag: YES\n", s.s, s.len)) _exit(20);
                substdio_put(&o,s.s,s.len);
        }

        substdio_put(&o,s.s,s.len);
        substdio_copy(&o,&i);
        substdio_flush(&o);
        _exit(0);
}