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Using IMF in Exchange for Spam Filtering

With Microsoft Exchange service pack 2, Microsoft has included IMF (Intelligent Mail Filtering) to help combat the legions of SPAM that plague our poor inboxes.  With this free tool, you’re getting what you pay for.  It’s simplistic and lacks many features that I would consider critical to a spam filtering solution (whitelisting, anyone??).  But it’s free, right?

A couple of my clients have started having problems with e-mails “not arriving” since SP2 was installed.  It seems the default settings for IMF definitely don’t meet what I would consider to be best practices.

Required Reading: Microsoft’s IMF Operations Guide.

Enabling and Disabling IMF

By default (in SBS), IMF is not enabled.   To enable (and subsequently disable) IMF filtering, start System Manager, then go to First Organization -> Servers -> <YOUR SERVER NAME> -> Protocols -> SMTP -> Default SMTP … -> (Right-click) Properties -> General Tab -> Advanced -> Edit -> Check Apply Intellingent Mail Filter.

Default Settings 

By default, IMF is set to “no action” when it blocks spam.  That’s probably not the best solution, if you’re looking to block spam.  I would recommend changing the setting to Archive and have it save all the spam it will be blocking.

The number of messages stored in your archive can build up very VERY quickly.  Make sure you have adqueate disk space in your archive location (by default it’s <Exchange Program Folder>Mailrootbadmail).  If you don’t have space there, move the mail store as per the instructions in Microsoft’s guide.

Monitoring and Manage Blocked E-Mail 

IMF does not include any tools to monitor and manage the e-mail it’s blocked.  Some quick searches came up with a great free tool called IMFCompanion that will help you monitor that ever-growing folder.  Remember that there’s no automatic way to delete the files, so you’ll have to go through and clean up the folder as part of your regular maintenance.

Updating the IMF

Microsoft regularly releases updates for the IMF. To have the IMF be recognized by Microsoft Update, you need to make a quick registry change.  The change is outlined in the Microsoft guide linked above, so I’m not going to rewrite it here.  Checking for IMF updates is something that should become part of your regular server update process.

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