Two (main) points you should know about.
1. Microsoft Support
It IS possible to publish the CRM Website for external access without using an IFD. Therefore you have only to route the site through your firewall. BUT this is no Microsoft supported scenario.
2. Outlook Client external access
If you are using the Microsoft Dynamics Outlook Client for CRM and you would like to use it from outside the corporate network, you have to configure the IFD.
Summary:
If you would like to use Microsoft CRM from outside your Intranet/VPN, you have to configure Form Based Authentication (CRM 4) or Claims Based Authentication (CRM 2011).
This is the statement from a Microsoft Engineer:
"Publishing the website to the internet and not using Claims/IFD is not supported. Even though the web client may still work it wasn't tested or designed to be run that way. We don't document all the things we don't support but rather the things we do like IFD/Claims authentication.
The outlook client will not work in this scenario.”
Cheers
