Q. I'm trying to connect to Microsoft Exchange Server 2010 with an Outlook 2003 client, but the connection is failing. What's wrong?

A. During the installation of Exchange 2010 Mailbox Server, you're asked if you have any Outlook 2003 or earlier or Entourage clients. If you answer no to this question, Exchange's mailbox creation doesn't create a public folder database, because Outlook 2007 uses the availability service instead of free/busy public folders. The lack of public folders shouldn't, however, stop an Outlook 2003 client from connecting—it just means functionality like free/busy won't work.

The actual problem is that with Exchange 2010 Client Access Servers (CAS), which are used for all client connections (including MAPI), all remote procedure call connections must be encrypted by default. Outlook 2007 and above automatically enable the encryption by default, but Outlook 2003 doesn't.

The easiest way to resolve this problem is to enable encryption between Outlook and the Exchange server on the Outlook 2003 client, as follows:

An alternative would be to disable the encryption requirement on the Exchange 2010 CAS, but this isn't recommended. You would do this with the following command in the Exchange PowerShell environment: 

Set-RpcClientAccess -Server savdalex10 -EncryptionRequired $false