[wellylug] SpamAssassin/Virus checking 'before' Exchange Server

Phillip Hutchings sitharus at sitharus.com
Mon Mar 29 14:03:39 NZST 2004


On 29/03/2004, at 1:51 PM, Jamie Dobbs wrote:

> Working in a company that loathes spending money I have been tasked 
> with
> finding a low/no cost solution to removing that large amoun of spam 
> that
> hits our Exhchange Server (5.5) on a daily basis.
> Changing to another mail server is not an option, but I was thinking 
> that
> perhaps a Linux box equiped with exim(or other MTA) + SpamAssassin + 
> some
> sort of antivirus might be a good answer to check incoming mail then 
> pass
> on to the Exchange Server once it passes spam and virus checks.
> Does anyone have any experience with such a setup or could point me to 
> a
> good online resource for this?
> I have tried Googling but haven't found anything or particular use so 
> far.

The theory isn't that hard. All you need is a mail server that accepts 
all mail to @yourdomain.com, checks it through SpamAssassin, if it gets 
higher than, say 7, drops it. Otherwise it'll just forward it through 
to the main server. All the major MTAs support this, though I couldn't 
tell you how to configure it.

I know there's a tutorial on tldp.org for running a postfix server 
doing almost this, except that the postfix server just forwards to 
another instance of postfix running on the msa port.

The only downside is that you wouldn't be able to check the existence 
of a user before accepting the mail, unless you somehow check with the 
exchange server. It's possible with Courier - just write a 
courierfilter that opens an SMTP connection to the exchange server, 
tries to send an email to the address and QUITs before sending DATA. If 
it gets an error, drop it, else run it through SpamAssassin and drop it 
if it's spam. The only downside is that courierfilter's can't modify 
messages. I would assume Postfix offers a similar ability.

--
Phillip Hutchings
me at sitharus.com
http://www.sitharus.com/




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