Basic Authentication
Turning off basic authentication on the EV VD's - I know that'd break external access to AE and Search Archive functionality (for exchange 2010, and I'm assuming the same for 2003 - or does it proxy those requests?)
What else would it break? Assuming all clients and exchange servers are trusted hosts. I'm not sure of all the Exchange configs in the environment, but I'm assuming if they're not using IWA between them, it'd break any retrival process too...
A fix has been found after some excellent work by a client resource -
The line add name="BasicAuthenticationModule" lockItem="true" /> has to be above <add name="WindowsAuthenticationModule" lockItem="true" /> in the applicationhost.config file.
If it is the other way around, Basic will supercede IWA regardless of what the client wants.