Hi, I would really appreciate help with 2 questions. First, does registry DWORD "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIS\ParametersSystem\Maximum Allowed Sessions Per User" (http://support.microsoft.com/kb/842022) work for limiting the number of MAPI connections on Exchange server? After setting this DWORD to 5, by changing IP address on a client I can make it open 7 and even 10 MAPI connections with Exchange. I am using our own tool to count MAPI connections, and I would like to test it by comparing with System Monitor. This leads us to the second question: how to monitor the number of MAPI connections using System Monitor? When I exit Outlook and restart MSExchangeIS, System Monitor at once shows 12 connections. What connections are they: MAPI, NSPI, anything else? Thank you, --LeonKh.

Hello Leon, Implement the following registry key which will cause Exchange to clean up the connections sooner. MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\KeepAliveTime Setting the value to anything between 1 and 7,200,000 milliseconds. Recommended value is 300,000 (5 minutes) Default time for Exchange is 7,200,000 (2 hours) See also 324270 324270 - How to Harden the TCP/IP Stack Against Denial of Service Attacks in Windows Server 2003 <http://support.microsoft.com/?id=324270> Also, please check your Network Card settings. If you have Windows 2003 SP2, then please install the update hotfix KB948496 or disable TCP Chimney Offload feature by running following cmd propmt netsh int ip set tcp chimney disabled. Please refer : http://msexchangeteam.com/archive/2007/07/18/446400.aspx Also, open Perfmonand add following counters Network Interface | Packets Recived Discarded Network Interface | Packets Recived Errros If you see these 2 counters and other Network counters then it will be an Network Card issue on the Exhange server, you may need to check you network port settings. I hope this info helps you a lot.

Hi Bala, How does one find out whether a NIC is offload-enabled or not? I can see that mine--Nvidia nForce Networking Controller--is checksum offload enabled. Is this the same thing? Also, when I came today--it means after about 10 hours of not touching my Outlook/Exchange test configuration--and looked at MSExchnageIS | Connection Count counter in Perfmon, it was still showing 15 connections. Any idea what connections could they be? Thank you for your willingness to help, --Leon.

Hello Leon, Thanks. I hope you are using Exchange 2003? Then Open ESM | Expand Mailbox Store | Logons | Click on View tab, add Total Ops. It will show you how many operations are running and tell which are clients it using, based that you can find how many clients are MAPI connections. TCP Checksum Offload and TCP Chimney Offload is slightly differ with each other, but action it will doare same. If this windows 2003 sp2, open the registry editior HKLM\System\CurrentControlSet\Services\TCPIP\Parameters Enable TCP Chimney - 1 Enable TCPA - 1 Enable RSS - 1 By default, when you install W2K3 Sp2, the value is 1 i.e., offloading is enabled. Set the value to 0 and reboot the server. Before disabling or setting the value to 0, you check how many connections are offloaded or In Host by running following command. netstat -t For MAPI sessions, you increase the value to 64, but it will have some performance issues on Exchange Server. However, we need to find why MAPI sessions are exceeding it can either problem with Network Port settings or NIC's on the server, by checking Perfmon counters for Network Interface. I hope this information help you.

Hi Bala, Thank you for the pertinent info. I think we are getting closer and closer to the solution. I've changed registry settings and reboot the server, but still see the same behavior as before. Maybe you could suggest what network port and NIC settings I should check? --Leon.