I came across this issue this weekend. According to Symantec, this seems to only affect SBS 2008 servers, but also could affect regular Exchange 2007 servers as well. Here is how to fix this issue:
To disable Exchange anti-spam agents:
- Open the Exchange Management console.
- Navigate to Organization Configuration -> Hub Transport in the console tree at the left hand side.
- Click the Anti-spam tab.
- Right click the Content Filtering Feature and select Disable
- Repeat step 4 for each of the rest of agents in the Anti-spam view.