We help IT Professionals succeed at work.

What are the rules employed by Outlook to mark email as Junk Mail

What are all the strategies/rules/filters/policies/techniques, whatever we call it as, employed by Microsoft Outlook to identify and mark an email as SPAM and moving it to "Junk E-mail" folder?

I'm not talking about the Junk E-mail Options itself available with Outlook like Safe Senders, Safe Recipients, Blocked Senders, etc. but various rules employed by Outlook to mark an email as SPAM and moving it to Junk E-mail folder.

Any relevant links on the same are also appreciated.  I hope there is a Microsoft Support knowledgebase article on this, but I don't have them handy with me now.

Experts idea/suggestion are welcome.

NOTE: The question is common across available Office versions - 2000, 2003, 2007
Watch Question

Sr. Systems Engineer
It really depends on your email server.. if you are connecting to your ISP with POP3 then outlook has it's own stand alone filter, if you are connecting to Microsoft Exchange then it works in concert with the settings on the Exchange server known as Spam Confidence Level.  It's a very complex thing and uses 'intelligent message filtering' way to complicated to get into and not known.. if people knew exactly how it worked spammers would use the info to get around it.

You can add a SCL or spam confidence level column to your outlook so you can see at least what outlook 'thinks' but there isn't any info on how it works again because spammers would use the info to get around the filtering- and that wouldn't be very smart for Microsoft to put out there...

Seeing the SCL (not sure this works if you aren't connected to Microsoft Exchange with your outlook, but it might)


Hi DeadNight,

Thanks for letting me know the existence of SCL and IMF settings in Microsoft Exchange server.


I've also found the Microsoft Support knowledgebase article that I asked about in my original question.

Here it is:

Description of the policy for how e-mail is filtered by the junk e-mail filters in Outlook or in Exchange Server

In INTRODUCTION section, they had clearly said "For the security of the junk e-mail feature, we do not disclose or discuss detailed information on a per-message basis."


As per DeadNight comment and also my opinion after me doing some research on this, it is not possible to find out how Outlook Junk E-mail filter works internally.


I found a question with answer similar to mine here:


NOTE: There is also a link to a PDF on how the Junk E-mail filter works, but it's by no means documentation of the product.