Microsoft hotfix offers selective Exchange IMF filtering

Microsoft has released a hotfix that updates Exchange Server Intelligent Message Filter's MSGFILTER.DLL component to allow select users' incoming email to be exempted from IMF processing.

One of the many limitations imposed by Exchange Server's Intelligent Message Filter (IMF) is the inability to include

or exclude individual Exchange recipients from filtering. If the IMF is in effect, all the mailboxes in the system have their incoming email screened by it.

However, Microsoft has released a hotfix (only available through Product Support Services (PSS) at this time, unfortunately) which updates the MSGFILTER.DLL component to allow designated inboxes to be exempt from IMF processing. Incoming mail sent to designated mailboxes, subject to certain restrictions outlined below, will not be processed by the IMF.

If you're a licensed customer, call Microsoft PSS and ask for the fix referenced in Knowledge Base article 912587, Exchange Server 2003 Intelligent Message Filter does not provide the functionality to exclude a particular recipient from antispam filtering, and Microsoft will send it to you free of charge.

Once you have the fix installed, you can create two kinds of IMF address lists: inclusive and exclusive lists. If Exchange IMF receives an email where all recipient addresses are on the exclusive list, the message won't be processed by IMF.

By contrast, if Exchange IMF receives an email where any of the recipient email addresses are on the inclusive list, it's not processed by IMF. However, you can only create and use one kind of list at a time. You cannot have both an inclusive and an exclusive list.

To create the inclusive list:

  1. Navigate to HKEY_LOCAL_MACHINE\Software\Microsoft\Exchange\ and add or edit a new key named ContentFilter.

  2. Within ContentFilter, add a DWORD value named CheckRecipients and set it to 2 (decimal).

  3. Also within ContentFilter, add a new Multi-String Value named RecipList.

  4. Edit the value of RecipList and add the emails to use, separated by line breaks.

  5. To create the exclusive list, follow the above instructions but set CheckRecipients to 1 instead of 2.

About the author: Serdar Yegulalp is editor of the Windows Power Users Newsletter.

Do you have comments on this tip? Let us know.

Related information from SearchExchange.com:

  • Tip: How to enable automatic Exchange IMF updates via Microsoft Update
  • Tip: Tune up your Exchange Intelligent Message Filter with IMF Tune
  • Tip: How to enable the Exchange Server Intelligent Message Filter on authenticated SMTP connections
  • Learning Center: The spamfighter's toolbox
  • 10 tips in 10 minutes: Spam and phishing exposed
  • Administration Guide: How to fight spam on Exchange Server

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  • This was first published in June 2006

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