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What are all the different ways to combat all forms of spam on Microsoft Exchange Server (2007 preferred)?

Types of spam may include:

  • Embedded image spam
  • malicious Zip file spam
  • Email with SenderID Status = None
  • Spam from hijacked computers
  • Spam from seemingly legitimate domains

I'm hoping this question can become the wiki for all the ways to deal with spam on Exchange.

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7 Answers 7

A powerful, free solution is ASSP http://assp.sourceforge.net/. All mail coming from outside the organization hits the ASSP server first and is filtered before being passed to the Exchange box. This works pretty well in our organization of about 800 users.

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It's not only specific to the server software, but also on the load on that server - spam percentage, amount of mailboxes, time of the year (around the holidays spam volumes increase dramatically) etc.

in one of the companies I worked for, we had 300 mailboxes and an internal exchange server, with another server running trend micro exchange scanner. The spam amounted up to 94% of incoming mail, and both the exchange server and the antivirus server were overloaded.

I installed a front end using CentOS+Postfix+SpamAssassin, using the following: - ~10 different RBLs reverse DNS lookups FuzzyOCR (for the image spam) Helo response delay of 15 seconds (this one cut off ~98% of the spam; requires a lot of extra RAM on the front end)

After this, the internal spamfilter on Exchange went down to less than 1% of the correspondence.

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On my setup, Im using HmailServer: http://www.hmailserver.com/ as our SMTP gateway, Enabled DNSBL, greylisting and Rules to filter Spam. More than 90% are all blocked with these alone, remaining are all handled by Exchange 2007 content filtering.

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I believe a question such as this should not be specific to any mail server software. While it would be nice to have it all in one package it's unfortunate that spam is such a great problem today that the most effective filtering is done by dedicated appliances.

I use the Open Source edition of Mailcleaner, which is a complete Debian based distribution specifically deigned as a spam and antivirus scanner. While this version is free it does require a little bit of work to get it working well, as there are no databases supplied for it to start with. It therefore requires feeding with known ham and spam, so that it can build the databases to use for filtering. For those less inclined to do such work there is also a commercial version, which is a little more "complete". See www.mailcleaner.org or www.mailcleaner.com for more information.

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We have used appliances from both Barracuda Networks and appliance-installs from Roaring Penguin (ie install a custom load of Linux on a server, the server essentially becomes an appliance).

We found that the Roaring Penguins, even as stand-alone, scaled much better under load (100K+ messages/day) than the barracudas did. We are evaluating a Roaring Penguin cluster now and the results are promising.

We found that the Barracuda offerings were much more user-friendly. The Roaring Penguins are much more configurable but it is way too easy for users to start filtering out too much.

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If you have a perimeter firewall, you should create strong rules to block mail ports in your network for all computers except for your email server. A complete list of email ports can be found here.

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1  
This would block mail altogether - not stop spam. –  Rex Apr 28 '11 at 16:20
    
What I was thinking about? Editing right now –  Miguel Apr 28 '11 at 19:32
1  
@Rex - technically this would stop spam as well. –  GregD Apr 28 '11 at 19:39
    
@GregD - very true (voted up for showing me up :) –  Rex Apr 28 '11 at 20:08

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