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Why is my Exchange Server connection on the fritz?

If the Exchange 2010 server disconnects and reconnects to Outlook, and it isn't a network problem, there are a few other areas to check.

While having Exchange Server disconnect and reconnect to Outlook is typically associated with network connectivity issues, it's possible this is an Exchange Server connection-related issue. The quickest way to determine the root cause may be at the client-level. You can enable Outlook 2010's logging feature to display connection details that will help diagnose Exchange 2010 connection issues.

To turn on logging:

1. Open Outlook 2010 and click the File tab

2. Click Options and then click Advanced

3. Select the Enable troubleshooting logging (requires restarting Outlook) check box

4. Restart Outlook

The title bar will indicate when logging is enabled on the Outlook client; you can reproduce the problem after that. Open the OPMLog.log file when the problem occurs; the path for this is C:\Users\username\AppData\Local\Temp\Outlook Logging\. If you find any error codes other than 0x00000000, you can research the codes and find the root cause of the Exchange Server connection problem.

If you have trouble reproducing the issue, you may be able to use the Connection Status feature to force a reconnect and generate log data.

1. Start Outlook and open the System Tray

2. Hold down the Ctrl key and right-click on the Outlook icon

3. Select Connection Status

4. Click on the Reconnect button

If your clients are in cache mode, the problem could be related to the OST file. If an OST file is corrupt, the Outlook client can't connect to Exchange while in cache mode. This is pretty easy to verify. Disable cache mode on the client and see if connection problems go away. If they do, you may be able to fix the problem by deleting the OST file and allowing Outlook to create a new one.

These Microsoft refrences may help if you're encountering a similar situation.

Understanding RPC Client Access

Troubleshoot performance issues in Outlook 2010

Even if the OST file is healthy, other factors could prevent it from working. If the mailbox size is greater than 5 GB and you're storing the OST on a hard drive, this could cause pauses, and these pauses could have the potential to create a disconnected state. To determine if your disk has a problem, there's a tool called Winsat you can use.

1. Run CMD as Administrator

2. Type Winsat Disk –Drive C –Ran –Write –Count 10 and press Enter

3. Verify the WinSAT score (Mbps). If value is greater than 15 Mbps, your disk is most likely OK. If it is less than 15 Mbps, you may need to upgrade storage to mitigate pauses and hangs.

If the disk performance is good and doesn't appear to be a client-side issue, investigate configuration and performance issues on the Client Access Server and Mailbox Servers in your organization. If you recently added or removed Exchange CAS, you may also want to ensure the RpcClientAccessServer attribute is configured properly on the mailbox databases where affected mailboxes reside. If you have a large number of concurrent mailboxes connected to Exchange, you may also want to make sure you haven't exceeded any of the Exchange Store Limits for Exchange 2010.

About the author: 
Richard Luckett is a consultant and instructor specializing in messaging and unified communications. He's been a certified professional with Microsoft since 1996 and has 20 years of experience in the public and private sectors. He's a Microsoft Certified Trainer with more than 15 years of training experience with the Microsoft product line and received the Exchange MVP award in 2006, 2007 and 2008. He's also an expert in deploying and integrating Exchange Server and Lync Server. He leads the Microsoft training and consulting practice at LITSG.

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How common are Exchange Server connection problems for you?

This issue happened to us very common in our client Outlooks. We opened a case to MS. They examined detailed DC, Exchange, Client outlook logs minutely and said that if there is firewall between DC - Exchange servers, FW drops connections that exceed 60 mins. because of this issue occured. (Our firewall drop timeout limit was 60 minutes). They advised us we need to enter a registry key -KeepAlivetime- on Clients, DC and Exchange servers that doesnt exceed 60 mins (we made it 50 mins as KeepAlivetime). Currently we are testing this solution  but can not verify. I hope it helps us