Hi Joakim,
You have to use External URL for customer locations to configure Outlook client.
For the internal Users you can use internal or external URL's to configure Outlook client.
You dont have to create Internal DNS. You can also use only one External URL for internal and external users.
Claims Authentication:
1. Needed for IFD access, when claim is enable both internal and internal access will need to pass through claims authentication.
2. External URL will be prompted for credentials
3. Internal URL will not be prompted for credentials.
Regards,
Khaja Mohiddin|||||http://www.dynamicsexchange.com/