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Many commercial-level antispam products are available for Exchange 2000 and 2003, but the majority of freeware antispam products are for mail clients rather than servers. However, freeware server products have started to appear that leverage the new spam-control technologies available in Exchange Server 2003, such as blacklists and reverse DNS checking.
One such product is Spam Sinker, an event-sink-driven system for fighting spam. Spam Sinker can work hand-in-hand with other, content-based spam control systems such as SpamBayes or the native filters within Outlook 2003. The program is free, and the author is willing to make customizations on a case-by-case basis for specific customers.
When installed and configured, Spam Sinker marks inbound messages believed to be spam with the same tags used within Outlook 2003 itself to identify spam. Rather than use heuristic detection, however, Spam Sinker concentrates on the validity of the sender -- i.e., by matching reverse DNS information against the sender's name and IP.
Mail is never deleted by the program, simply marked as spam, and can therefore be used not only by Outlook 2003 users, but by any mail client that can sort by headers. So not only POP3 users but IMAP and OWA users can benefit from it.
Spam Sinker allows for whitelisting and blacklisting of messages, and has two varieties of each: hard and soft. Hard blocking disallows messages from IP addresses that are in the program's XML configuration file, while hard-allowing forces a message to be recognized as good if its IP is in a known-good pool. No detection is performed on hard-screened messages. Soft-allow and soft-block lists, on the other hand, are built during message detection, and evolve over time. The program can also match against any number of third-party DNS blacklists.
You can download Spam Sinker here.
About the author: Serdar Yegulalp is the editor of the Windows 2000 Power Users Newsletter and a regular contributor to SearchExchange.com.
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This was first published in December 2004