In Exchange 2013 you can set an email to be put in the user’s Junk E-Mail folder based on if you think it is SPAM or not. This doesn’t use the Exchange built in spam filtering, it assumes you have a spam filter external to your Exchange environment that can tag an email that it thinks is spam or possible spam.
In my case we had a Barracuda Spam Firewall, this would pass messages with a spam score of 0 to 3.5, would tag messages with a spam score of 3.6 to 5.9 and block 6 and over. The tagging involved adding [POSSIBLESPAM] to the subject line and sending the message on to Exchange. This caused some confusion to users who wondered if it was spam or not and also didn’t want it in their inbox. So to configure this you need to use transport rules in Exchange, here’s the process:
1. First your anti-spam product will need to tag the subject line with [POSSIBLESPAM].
2. Within Exchange create a transport rule as shown below, this should come before all your other rules (probably).
This rule catches any messages with [POSSIBLESPAM] and then setting the SCL tag of the email to 8.
3. Now at this point Exchange needs to be checked to ensure it will process the SCL tag of the email accordingly. The documentation for Exchange says that email which has a an SCL tag of 7 or over for the configured SCLJunkThreshold say, will be sent to Junk Email. However I’ve found it means an SCL tag of over 7, i.e. 8 and above.
4. Configure the -SCLJunkThreshold to 7 with this command:
set-OrganizationConfig -SCLJunkThreshold 7
5. Now test that the a message which is tagged ends up in your Junk mail folder within Outlook. If its tagged with [POSSIBLESPAM] its set with an SCL of 8, and the message stuck in the Junk email folder.