Mail is not being scanned and the message totals in the Activity Monitor aren't being updated. When you check the Windows event log, it lists several instances of event 57 with the following details:
Error code 0x80040154 in transport post categorization sink.
First seen in
PureMessage for Microsoft Exchange, version 3.0.x
What To Do
On the Exchange server, open a command prompt and run the following command:
regsvr32 "C:\Program Files\Common Files\Microsoft Shared\CDO\cdoex.dll"
This will register the cdoex.dll file and resolve the issue.