New Outlook client will not connect to Exchange 2010, but OWA works perfectly. Existing Clients Connect without a problem.

When I connect a new client to my Exchange 2010 server, I get the message "Unable to open you default e-mail folders. The Microsoft Exchange Server computer is not available. Either there are network problems or the Microsoft Exchange server computer is down for maintenance."
All other clients that were existing in the past can connect without an issue, but no new clients can connect. It doesn't matter what version of Outlook. BUT - I can connect using the OWA client to that user without any problem. Even if any firewall is turned off, still no connection can be made.
There are no errors in the Windows event log, Exchange event log, or the local workstation that tries to make a connection. All workstations are on the same subnet and connected directly via 1GB switch joined to the same domain.
Running Exchange 2010SP1 on Server 2008SP1.
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Do you have any DNS server entries on the client PC NIC config other than your internal DNS server?

Go to Control Panel -> Mail applet and change the settings for the Profile or Outlook setup.
Click the Change button, then on the screen with Mail Server and Mailbox click the More Settings button.
Go to the Security tab and put a checkmark in the Encryption box area.

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Time to test outlook autoconfig:
With outlook open, hold down CTRL key and right click on the Outlook icon in the bottom right hand side of your screen, then on the popup menu select the "Test Autoconfiguration". Select that, enter valid credentials and select the "autodiscover" option only and test.

Report back any errors or error codes you see in the log.

Also check your Outlook settings and make sure that it is not set to connect over HTTP first and the Exchange server name listed, when pinged internally returns the INTERNAL IP address of your mailbox server
marcmeshurleAuthor Commented:
Chakko - your suggestion corrected it in seconds. Even within the local subnet, Exchange 2010 requires encryption between the client and the server, not previously required in Exchange environments.
Points to Chakko.
marcmeshurleAuthor Commented:
Very quick resolution! Worked perfectly.
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