OMA - Error 400 - Unable to connect to your mailbox   

I have been completely unsuccessful in setting up OMA on our exchange
server. OWA works just fine and has been doing so for some time now. -
This is an SBS2003 (upgraded from sbs2000) with Exchange 2k3 SP2 (also
tried with SP1) and Win2k3 SP1 and SBS2k3 SP1 (and Sharepoint SP1).

logon domain if testdomain.local, smtp domain is testdomain.com

When trying to access via IE6, at http://testserver/oma (or https) I
receive the following error:

Unable to connect to your mailbox on server TESTSERVER. Please try
again later. If the problem persists contact your administrator.

Searching news and web, there are a number of references to this error,
but only _3_ for a status code of 400 (most are for the 403 -
kb817379).

Lets see, in order to cut down on the the basics, here is what has been
verified according to kb docs and others sources.

* .net framework (re)install:  "aspnet_regiis.exe -i"
* Enable kerberos authentication:
"cscript adsutil.vbs get w3svc/1/NTAuthenticationProviders" ==
NTAuthenticationProviders       : (STRING) "NTLM,Negotiate"
* Configured service principle name (did all to be safe):
 setspn -A HTTP/testserver testserver
 setspn -A HTTP/testserver.testdomain.local testserver
 setspn -A HTTP/testserver.testdomain.com testserver
* Added the required lines to the web.config file in the OMA\Browse
directory according to http://support.microsoft.com/?kbid=823265
* /OMA, exchange-oma, microsoft-server-activesync, Exchange, Exchweb,
Exchadmin have all beem excluded from sharepoint
* Mobile access IS enabled globally and individually
* Exchange**AplicationPools are both set to LOCAL SYSTEM
* ExchangeVDir key is set to the proper exchange-oma vdir
* exchange-oma vdir has SSL off (makes no difference either way though)
* Forms auth is turn off on on the Exchange Virtual Server
* Default Recipient Policy is set correctly
* I've cleared the host headers to <All Unassigned> 80 ""
  (i've also tried adding specificaly for the server <All Unassigned>
80 testserver, <All Unassigned> 80 testserver.testdomain.com, <All
Unassigned> 80 testserver.testdomain.local) made no difference
* OMA vdir is set to basic authentication, domain is set to testdomain

I've included the eventlog entry, pretty much everything relating to
this (with 400) has been unresolved.  The threads just seem to have
died, can anyone help me with this?

---------------------------
Category 1000, Event 1805

Request from user j...@testdomain.local resulted in the Microsoft(R)
Exchange back-end server TESTSERVER returning an HTTP error with status
code 400

Response:
Date: Mon, 13 Mar 2006 20:33:32 GMT
Server: Microsoft-IIS/6.0
MicrosoftSharePointTeamServices: 6.0.2.6361
X-Powered-By: ASP.NET
Cache-Control: private
Content-Length: 0
Public-Extension: http://schemas.microsoft.com/repl-2

Original Request:
Content-Type: text/xml
Depth: 0
Content-Length: 389
Expect: 100-continue
Connection: Keep-Alive
Host: testserver

For more information, see Help and Support Center at

date: 13 Mar 2006 15:49:47 -0800   author:   unknown