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Integrating any Anti-Spam Filter into Exchange

Alexander Zammit

Alexander Zammit Photo

A Software Development Consultant with over 20 years of experience. Many of his projects involved Exchange integrated applications, including a FAX server, a mail security product and anti-spam products.

  • Published: Sep 27, 2005
  • Category: Anti-Spam
  • Votes: 5.0 out of 5 - 2 Votes
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Can SpamAssassin filter emails to the Outlook Junk Email folder? What about applying Outlook Safe Senders/Recipients and Blocked Senders to an anti-spam firewall appliance? Is it possible for anti-spam solutions running on Linux gateways to integrate with Exchange just like the Intelligent Message Filter does?

Mapping Results with IMF Tune

IMF Tune provides the missing link. It is able to extract the filtering result and map it to an SCL. Let's see how we can get spam to be routed to the Junk Email Folder.

IMF Tune is an extension to the Exchange Intelligent Message Filter. Thus you would first start by installing IMF Tune and IMF on the same Exchange server. Note that as from Exchange SP2, IMF is an integral part of Exchange and there is no separate IMF install. Check the references section for all relevant links.

Next you need to configure IMF. I will assume you already know how to do this, otherwise check the references. To keep things simple I won't activate IMF gateway blocking. Thus I will set the gateway action to 'No Action' and the gateway threshold (which is irrelevant) to 9.

What is more interesting to us is the Junk Email threshold. I will set this to a relatively high value i.e. 6. This means that emails with SCLs greater than 6 will be deposited to the Junk Email folder.

The reason for this high threshold is the fact that here I am not really interested in IMF filtering. I will instead rely on the anti-spam filter sitting in front of Exchange.

Intelligent Message Filter Configuration

Of course don't forget to enable IMF from the Exchange System Manager under the SMTP Protocol. Note that as from SP2 IMF enablement was moved to SMTP Virtual Server | General | Advanced.

Next we configure IMF Tune. Open the configuration, select the SCL Management category and Click on Add. This opens the SCL Mapping dialog

IMF Tune SCL Mapping

What we configure here depends on the type of email classification supplied by the spam filter. If we consider the Yes/No header flag discussed earlier, then we would set:

Header Name: X-IS-SPAM
Matching Type: is exactly
Header Value: yes
Operation Type: set value to
SCL Value: 7

Next save the new mapping and select the IMF Tune General category. Here make sure that SCL 7 is configured as Accept. Otherwise IMF Tune itself might block email delivery.

Handling of SCL 7

That's basically it. Save changes and emails identified as spam will be routed to the Junk Email folder. Furthermore any Safe Senders/Recipients, Blocked Senders configured at the client will also be applied. As promised at the introduction there will be no difference between spam filtered by IMF and spam filtered at the edge.

IMF Tune through the SCL Mappings dialog also caters for more complex email classifications. For example we could search for a tag within the Subject or within any other email header using the 'contains' matching type. Of course the more complex the classification the more complex the configuration gets. So in general one should look at rendering this information as easy to process as possible.

For brevity here I described the setup of IMF and IMF Tune at one go. In general it is easier to first setup IMF, test it out to make sure it works properly and then proceed with IMF Tune.

To conclude, I want also to remind you of the classic Junk Email enablement problem that many run into. For emails to be deposited to this folder, it must be enabled on each mailbox. I discussed solutions to this issue in a recent article Centralizing Junk Email Folder Administration


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