If the application is Outlook, you may see the following events in the Application event log of the client computer:
Event ID: 25
Task Category: None
Description:Could not perform the desired operation. The selected command is not valid for this recipient. The connection to Microsoft Exchange is unavailable. Outlook must be online or connected to complete this action..
Event ID: 26
Task Category: None
Description:Connection to Microsoft Exchange has been restored.
- Verify the configuration of the network device, per the vendor recommendations or through contacting the Technical Support team for the vendor. This may require increasing the timeout on the network device so that long running connections are not prematurely closed.
- For an application server connecting to Exchange Server 2010, set the application server's TCP Keep-Alive time to a value less than the idle connection timeout window on the network device.
For example, if the idle connection time out on the device is 15 minutes, set the TCP Keep-Alive on the application server to a value less than 15 minutes.
In many cases, session timeout settings are typically too low. In discussion with network device vendors, it is frequently recommended that RPC timeout settings should be 120 minutes, at a minimum.
Note A frequently used test to determine whether a device configuration is at issue is to bypass the device. This is done by using a Hosts file on the client or a DNS record to access a single CAS server in the array. However, if the device is also used as a gateway, this may not provide accurate results.
For additional information on long running connections, see section 18.104.22.168, TCP Keep-Alives, from the following Internet Engineering Task Force document:
For additional information on Load Balancing for Exchange Server 2010, see the following presentation from TechEd 2011
Article ID: 2535656 - Last Review: Mar 20, 2014 - Revision: 1