Your outlook 2003 client will not connect to to exchange 2010, this is down to encryption, or you can disable exchange 2010 excryption or configure the client as seen below.
This is down to exchange 2010 requiring encrypted connections.
To configure outlook 2003 follow these instructions.
- Go to control panel > Mail > Show Profile > <Select Profile>
- Select Properties > E-mail Accounts > View or Change existing e-mail accounts
- Click Next > Microsoft Exchange Server > Change > More Settings > Microsoft Exchange Server > Security
- You then need to put a tick in check Encrypt data between Microsoft Office Outlook and Microsoft Exchange Server, this should resolve the issue
- Select OK to all remaining screens..Additionally you can edit the reg key in the registry with the following key.HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\11.0\Outlook\RPC