Simultaneous mapi connection (from windows XP) to CAS server

Hello Guys,

Here is my environment : 4 CAS, 12 MBX and 4 HUB, 4 LYNC. I have an heterogenous machine environment (windows 7, windows XP with Outlook 2007/2010 for both)

I have set static port for RPC connection to CAS. OAB are web-based distribution and public folder distribution is enabled.

I've noticed that: from Windows XP, user that opened Outlook 2007/2010 simultaneous MAPI connections (port 7374) are established on CAS server... and this is making my CAS working too much...

From windows Serven, user that opened Outlook 2007/2010 only one connection is established... I think the issue might be linked with the OS but I can't find out.

Also I have the same issue with the ucmapi.exe from lync. It's opening simultaneous ucmapi connection to CAS.

Any idea?