Many modern e-mail servers do not have any standard functions for e-mail messages filtering. Recently, the Microsoft Corporation has issued an extension module for an exchange mail server that is called Exchange Intelligent Message Filter. This module provides a control of the e-mail messages stream; though some basic features, such as an attached files blocking function, should be implemented in the standard configuration of each server. The simplest functions for the attached files blocking significantly decrease time of system administrators for the viruses' elimination. There are some solutions that could protect your server from the stream of viruses and spam efficiently.
A mail retranslator or a proxy server is often used for protecting the computers from doubtful attached files, spam and other e-mail violators. Distributing functions of storing e-mail messages and e-mail deliveries between the exchange mail servers and the mail retranslator increases a level of security and performance as well. If the mail retranslator is displaced in a demilitarized zone (DMZ) of the network, then you can avoid any communication with the mail server from the outside.
For the e-mail retranslator you should allow the SMTP traffic to pass via the mail server port TCP 25 into the retranslator or proxy server inside the DMZ. Furthermore, you should set a connection of the mail server behind the firewall with the proxy-server via the SMTP. Delegating the tasks like the spam filtering and the attached files blocking to the proxy-server permits to decrease the loading of the exchange mail server processor.
An open source proxy-server, Fluff SMTPGuardDog, is one of the systems that can solve such tasks sufficiently. This is an open system for filtering the e-mail for the Windows 95 and higher. The Fluffy is between the Internet and the e-mail server and it checks all incoming messages and filters all unsafe attached files and spam.
The Fluffy does not require any high calculating power. The software author states that 233 MHZ Pentium can handle about one thousand and five hundred messages for ten minutes. The Fluffy can work at one PC with the exchange mail server or in the DMZ of the dedicated system.
The Fluffy does not work as a service and that is the reason why during the installation, you should register in the system and run the Fluffy as a desktop application. Nowadays, it is an only possible mode of the Fluffy work. Therefore, some users claim that they have succeed in running the Fluffy as a service with the help of the Srvany utility from the resources complex or use the filter as a scheduled task at the initial loading of the computer.
Actually, the Fluffy installation process is not very complex, as it can be performed by people, whose knowledge in the Windows system is not very high. However, additional settings of this proxy server should be performed by skillful system administrators to achieve a more productive e-mail processing and filtering.
Since the Fluffy is displaced in the intermediate level between the exchange mail server and proxy server, it is a good solution due to its performance. It meets all security requirements and can provide a significant support for the system protection.