Unable to connect Outlook 2003 to Exchange 2010

Articol scris de  Paul Roman (MVP for MS Exchange)

When you try open an email account located on an Exchange 2010 server using Outlook 2003 you will get the “Unable to open your default e-mail folders” error. If you try to connect to the same mailbox using Outlook 2007 or Outlook 2010 beta version you can connect without any problems.
This is caused by the fact that in Exchange 2010, by default, you need an encrypted conection to access the server. In Outlook 2007 and later this is the default setting but in previous versions this was optional.

To solve this issue, you have two options:

1. You configure your email client to use encryption (recommended). You can do this by accesing your email profile and check the “Encrypt data between Micrososoft Office Outlook and Microsoft Exchange” as you can see bellow:

2. Or you can disable the encryption on the Exchange 2010 Client Access Server using the following cmdlet (not recommended):

Set-RpcClientAccess –identity <ServerIdParameter> –EncryptionRequired $false

Usually I would go with the first choice. It is more secure and there is no reason not to do it. If you need to configure a large number of computers you can always use Group Policy. You can find more info about GPO templates for Office 2003 here:
http://office.microsoft.com/en-gb/help/HA011402401033.aspx