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WinDeveloper IMF Tune
WinDeveloper IMF Tune

IMF SCL Configuration - getting it right

Alexander Zammit

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Alexander Zammit has been developing server applications for over 15 years. Most of his works involve Exchange integrated applications, including a FAX server, a mail security product and anti-spam products.

  • Published: Feb 28, 2005
  • Category: Anti-Spam
  • Votes: 4.9 out of 5 - 13 Votes
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Correct SCL configuration is the key to a successful Exchange Intelligent Message Filter setup. With a good understanding of SCLs we can get the best results out of IMF. In this article I look at how to do this with the help of windeveloper IMF Tune, a freeware application released for this purpose.

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>

IMF Settings

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:

SCL Ranges

Enabling of IMF per virtual server is done from:

<Organization> | Servers | <Exchange Server> | Protocols | SMTP | 'Intelligent Message Filtering'

Enable IMF

User Comments - Page 1 of 1

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Scott E. S. 12 Jan 2010 07:51
Thank you for the information, after re-reading the site, I have come to realize that I had understood the SCL rating's backwards. Thanks
Alexander Zammit 11 Jan 2010 14:01
I think you should start from the SCL thresholds. With 8/8 you will be allowing a lot of spam to reach your inbox. The HIGHER the threshold the LESS spam you will block.

A more common threshold setup is:
Junk: 4
Gateway: 7

Of course you have to fine tune your settings, but this is certainly a more realistic starting point.
Scott E. S. 11 Jan 2010 13:41
Does anyone have any information on blocking specific word-groups that IMF doesn't catch? Even with SCL rating at 8/8, my Exchange server is still getting spam from e-mails that break-up and split key words.... Example: Pe nis erec tion for four hours. It stops my previous filter from working. Any ideas?
walt 13 Oct 2009 17:23
so it is freeware or what?
Scott S. 22 Jul 2009 10:32
Nevermind....I just had to slow down and reread...bummer. I'm a newbie to IMF so really could have used this. So far though, it's been pretty simple to implement and haven't gotten any FP's with 7/6 settings.
Scott S. 22 Jul 2009 10:29
I went to download the IMF Tune utility and it doesn't say that it's freeware.. Did this change?
Alexander Zammit 22 Apr 2009 05:24
The article is correct. The problem is the typo at the UI as explained here:

The text "Move messages with an SCL rating greater than or equal to:" should read "Move messages with an SCL rating greater than:".
Jisha haneefa 22 Apr 2009 05:14
Please verify the email classification once again.It should be as:

1)Emails moving to inbox-------SCL0 to Junk Email SCL-1
2)Emails moving to Junk email--Junk Email SCL to Gateway SCL-1
3)Gate way action(reject, delete or archive emails)----Gateway SCL to SCL 9
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