Cannot connect to SBS 2008 Exchange with Outlook externally

Question

Hello,
We used to be able to connect to a native Exchange account with Outlook even when we were not onsite, however this has stopped working.
If we connect onsite, it works straight away.
Outlook Web App works fine.
We are using a self-signed certificate and always have.  It is still on the same certificate since it was last used successfully (i.e. it hasn't expired and been renewed).
Any thoughts? Thanks.

Answer 1

Plain white screen is expected result.
Lets add a registry key if not exist
1. Set DisableLoopbackCheck in registry :
2.  Click Start , click Run , type regedit , and then click OK . 
3.  In Registry Editor, locate and then click the following registry key:  HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa 
4.  Right-click Lsa , point to New , and then click DWORD Value . 
5.  Type DisableLoopbackCheck , and then press ENTER. 
6.  Right-click DisableLoopbackCheck , and then click Modify . 
7.  In the Value data box, type 1 , and then click OK . 
8.  Quit Registry Editor, and then restart your computer. 
Also Create BackConnectionHostNames
Open Registry , Under HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0
1) Create Multi-String Value “BackConnectionHostNames”
2)  Right-click BackConnectionHostNames, and then click Modify.
3) In the Value data box, type 'Externalhostname'  (Note - ExternalHostname is the name that is shown in Get-Outlookanywhere result)
-RPCwithCert VD By default, all authentication methods are disabled
SSL required
Require 128-bit encryption
-On RPC virtual directory enable
Basic authentication
Windows authentication
SSL Not required
Default Authentication Settings :-
https://technet.microsoft.com/en-us/library/gg263433(v=exchg.80).aspx