Note: This article makes references to WinDeveloper IMF Tune, an application that was available as freeware at the time of writing. IMF Tune is today a commercial product.
The Intelligent Message Filter IMF, is one of the anti-spam products with the least configuration settings I ever came across. It boils down to four settings, Gateway SCL, Gateway Action, Junk Email SCL, and enabling of IMF per SMTP virtual server. The lack of options may easily give the impression that the configuration is trivial.
Recently, a client for whom I was developing some software, installed IMF. He came across the most common problem in setting it up. What values should the SCL settings have? This question led me to develop a new freeware application, WinDeveloper IMF Tune, that helped him getting the settings right. So today I would like to discuss the use of this application with the hope that it can be of benefit to many others.
What's an SCL by the way? The SCL rating is a value from 0 to 9 assigned to emails as a classification of their likelihood of being spam. 0 indicates lowest probability whereas 9 indicates near certainty of the email being spam. Values in between indicate a varying degree of certainty.
Given the SCL value, an administrator is expected to decide what to do with the email. Emails with ratings at the lower range of SCL values are typically permitted to go through as valid email. High SCL ratings enable Administrators to be brave and take drastic actions such as delete, reject or archive. Values in between typically require emails to be deposited to the Junk Email folder for verification by the end-recipient. So effectively our goal is that of identifying these three SCL value ranges. Getting them wrong may lead to many valid emails ending in the Junk Email folder. Getting them totally wrong (and some do!!) may lead to loss of valuable emails.
Quick IMF Configuration Tour
Before delving deeper into SCLs, let's have a very quick look at the IMF configuration to make sure everyone is in sync. The main IMF configuration settings are available from:
<Organization> | Global Settings | Message Delivery <properties> | Intelligent Message Filtering <property sheet>
Here you will find Gateway SCL, Gateway Action and Junk Email SCL. The Gateway settings are used to filter emails scoring very high SCLs. At this end one can configure IMF to reject, delete or archive emails. The Junk Email SCL identifies the emails that should be deposited to the Junk Email folder. Obviously this is set to a lower value than the Gateway SCL. Note that there is a typo in the IMF configuration. The text "Move messages with an SCL rating greater than or equal to:" should read "Move messages with an SCL rating greater than:". Combining these two SCL values we end up with three buckets for email classification as depicted below:
Enabling of IMF per virtual server is done from:
<Organization> | Servers | <Exchange Server> | Protocols | SMTP | 'Intelligent Message Filtering'