SPAM filtering with Exchange 2007 and ForeFront

I’m the sysadmin for a small company that uses exchange 2007 and forefront for their spam protection. Recently quite a bit of spam has been coming through and I’m looking for ways to tweak the settings. All of this was set up by a technician before me and this is my first go at Exchange 2007 and ForeFront. Antispam tools have been enabled in Exchange 2007

My question is, when messages arrive, which system scans them first and what would the workflow look like? Does exchange take them in and if they pass Exchange’s antispam tools then forefront passes the message through its rules?