[There's a reason that Yoda is the unofficial mascot of SBS.  Size indeed matters not.] Exposing the SCL to better understand your "SPAM" ranking - THE OFFICIAL BLOG OF THE SBS DIVA
Wed, May 26 2004 18:13 bradley

Exposing the SCL to better understand your "SPAM" ranking

http://blogs.msdn.com/exchange/archive/2004/05/26/142607.aspx   Well the EHLO blog comes through once again with a cool post about how the SCL [spam ranking] can be exposed to help a user better understand the filtering process. 

This is interesting... this seems backwards to me “This array allows you to choose how aggressive or conservative you want your spam filtering to be by selecting a threshold value above which you consider a message to be spam. If you want to aggressively filter spam, you can choose a fairly low threshold, such as an SCL value of 5, which would catch a higher number of spam messages. However, a higher number of false positives would also be caught. To filter spam more conservatively, you can choose a higher threshold, such as an SCL value of 8, which would catch fewer spam messages, with a lower number of false positives being caught.“

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/e2k3/e2k3/ast_spam_confidence_level.asp

So putting a higher value on that SCL setting does not mean that you'll catch more spam, it actually means you'll catch less spam.

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# re: Exposing the SCL to better understand your "SPAM" ranking

Friday, May 28, 2004 4:18 PM by bradley

This actually makes sense. A low SCL value means a low probablility of it being spam. Conversely, a high SCL value means it's almost certain to be spam. I like to think of it as this formula: (SCL x 10) = % chance it's spam.

If you set the threshold to a value of 8, what you're doing is telling IMF to filter out anything with a value of 8 or higher. So, with the formula above, if you have a mail that comes in and is stamped SCL=9 (think of that as 90% chance it's spam) you're going to filter it out. An SCL=7 (70% chance), we don't. Very conservative filtering.

Set your SCL threshold too low (say 3), then you're going to be filtering out mail that is perhaps only 30% likely to be spam -- lots of false positives!

# re: Exposing the SCL to better understand your "SPAM" ranking

Friday, May 28, 2004 11:04 PM by bradley

Okay so maybe it's just the wackobeancounter that thinks it's backwards...everyone else thinks it's fine. :-)

# re: Exposing the SCL to better understand your "SPAM" ranking

Monday, June 28, 2004 4:50 AM by bradley

Just FYI, I collect % confident for 5+ SCL score

X-SCL: 5 72.63%
X-SCL: 5 82.13%
X-SCL: 6 86.33%
X-SCL: 6 89.08%
X-SCL: 7 92.88%
X-SCL: 7 97.32%
X-SCL: 8 97.54%
X-SCL: 8 99.3%
X-SCL: 9 99.61%
X-SCL: 9 99.89%
X-SCL: 9 99.9%