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Document ID:	466
Subject:	How to filter outbound messages for spam when used as a firewall for MS Exchange or any other SMTP server
Creation date:	4/23/09 4:34 PM
Last modified on:	10/7/10 10:37 AM

How to filter out-bound emails for junk/spam

Outbound messages are filtered when you use Xeams as your out-bound SMTP server. If Xeams is the only server on your network filtering out-bound messages is easy. However, if you have other servers, such as Microsoft Exchange, the network configuration may become tricky.

The following section lists different network designs that are typically used in companies.

Using Xeams as a firewall for a primary email server running on the same machine

Assumptions:

• Xeams is running on the same machine that is used by your primary email server, which could be any server that supports SMTP, for example MS Exchange.
  
  
• Your primary server has a feature to forward all out-bound message to a one machine. The feature is called Smart Host in MS Exchange.
  
  
• You are using SMTP Proxy Server in Xeams to process incoming emails. The actual email server is configured to listen on port 2500 for SMTP traffic. In coming emails come in to SMTP proxy server on port 25, which is then proxied to port 2500 of your actual server.
  
  
• The IP address of your machine is 192.168.1.5
  

End goal:
Xeams comes with two SMTP servers:

• SMTP proxy server
• Normal SMTP server

In this example, SMTP proxy server is already configured to receive in-bound emails. The goal is to enable the normal SMTP server to listen for out-bound emails.

Steps:

• Create a new IP address for your machine - Since the SMTP proxy server is listening on port 25, you need to create a new IP address for the machine. This is required because two servers cannot listen on TCP/IP port 25 on the same IP address. Assume the second IP address is 192.168.1.6. Click here to learn how to create additional IP addresses. You do NOT need another network adapter.
  
  
• Configure Xeams SMTP server to listen on port 25 on the second IP. Log in to the Admin Console and click Configuration link for the SMTP server.
  
  
• Check the Enable box, set the port to 25, and select 192.168.1.6 from the Bind To pick list.
  
  
• Add the IP address of your primary server (Exchange) to the Open Relay list, under the Relaying tab. Since out-bound messages are sent to domains other than your local domains, relaying is required.
  

The following images show the network diagram before and after the change.

BEFORE	AFTER

Common configuration error

Often administrators set Exchange's smart host to point to the same IP address where the Proxy server listens on (192.168.1.5 in this example), which is incorrect. Remember the SMTP Proxy server is configured to send every message to the actual SMTP server (Exchange in this case). Therefore, using the proxy server's IP address in smart host creates an infinite loop and you email will never go out.

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