Question: ```
local_machine:$> ssh myself@external_machine_ip_address -p specific_port -X
external_machine:$> echo $DISPLAY
localhost:10.0
external_machine:$> emacs
Warning: Cannot convert string "-*-courier-medium-r-*-*-*-120-*-*-*-*-iso8859-*" to type FontStruct
Warning: Cannot convert string "-*-helvetica-medium-r-*--*-120-*-*-*-*-iso8859-1" to type FontStruct

```

I do see the emacs window, but I can't see any of the characters. What could be the error ?

Answer: 
Exchange is using the same kind of authentication/authorisation as, for example, file shares.

When you connect with an appropriately configured transport (Named Pipes are the simplest) then your authentication information is carried across. In a domain (required for Exchange) this uses Active Directory's Kerberos derived system that means you password (or a hash of your password) is not sent, but rather a token that AD gives you computer. The Exchange server then checks that token with an AD to verify you identity.

See [Kerberos](http://en.wikipedia.org/wiki/Kerberos_%28protocol%29) for more information.

(NTLM also provides SSO in a similar way, but it has some security problems and has been replaced by Kerberos in most places.)
The system is what's known as Single Sign On (Wikipedia artice [here](http://en.wikipedia.org/wiki/Single_sign-on)).

Exchange is the back end system for outlook in most enterprise environments and it integrates very tightly with the active directory in Windows Server.