If you are using the native Exchange 2013 anti-spam settings, you may also want to configure how the users are handling their junk mail and what the thresholds are for sending messages to their Junk folders. Since none of this is found in the GUI anymore, it’s helpful to know the PowerShell commands.
What I typically do when setting up a new Exchange 2013 server that is going to handle its own anti-spam settings is to first enable the anti-spam components. I do that by running the install-antispamagents.ps1 script in the Scripts directory from an escalated Exchange PowerShell prompt.
Once that’s done, I run the following to set the basic SpamConfidenceLevel to 8 and to reject messages for the ContentFiltering agent: Read more