When running a manual or scheduled scan with SMSMSE on Exchange 2010 and later, SMSMSE uses the Exchange Web Services (EWS) interface to request items from Exchange for scanning purposes. 

By default, SMSMSE will use 5 EWS threads for these types of scans, meaning it can request 5 items from Exchange simultaneously. Scan throughput can be increased by increasing the number of threads, but keep in mind this may affect EWS performance as the SMSMSE service will use more of the EWS resources on the Client Access server.

To adjust the number of EWS scan threads:

1. Open the registry editor (Start -> Run, regedit).
2. Navigate to:
   (SMSMSE 7.9.x & Later) HKEY_LOCAL_MACHINE\SOFTWARE\Symantec\SMSMSE\<version>\Server
   
   (SMSMSE 7.5 & Earlier) HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Symantec\SMSMSE\7.x\Server.
3. Create a new DWORD value called ScanJobThreadCountDword, and set the value to the desired number of scan threads. Typically this should be limited to the number of Scan Processes configured for SMSMSE under the Admin -> System Settings section of the SMSMSE console.
4. Restart the Symantec Mail Security for Microsoft Exchange service.