This Knowledgebase article provides information about reducing the replication burden on the passive server by omitting the transient files in the Exchange Log directory during replication.
IMAPI clients, such as Outlook Express, create transient STF files during attachment downloading in the Exchange Log directory for Microsoft Exchange 2000 and 2003 versions, which by file filters default are replicated. To reduce the replication burden, Exchange filters should be modified to exclude these files thereby minimizing replication traffic.
The Exchange filters for the Log directory, by default, are wildcards as shown below:
<log directory location>\**
e.g. d:\program files\exchsrvr\mdbdata\**
The Exchange filters for the Log directory should be modified to reflect the following:
<log directory location>\*.log
<log directory location>\*.chk
e.g. d:\program files\exchsrvr\mdbdata\*.log
Neverfail for Exchange 2007-07-11 and prior
http://support.microsoft.com/default.aspx?scid=kb;en-us;258542 -'XADM: .stf Files May Appear in the Folder That Contains Database Log Files'