We use Outlook 2010 with latest hotfixes + Exchange 2010 SP2 ctrl+rightclick on Outlook icon + check autodiscover shows basic authentication & after several seconds same operation shows NTLM! Clients recieve authentication popups during the day :( Tried resetting Virtual directories, configuring outlookanywhere with both -ClientAuthenticationMethod & -IISAuthenticationMethods = NTLM get-outlookanywhere -server cas01 RunspaceId : dd546129-3302-4011-8ccc-b73ea2909785 ServerName : CAS01 SSLOffloading : False ExternalHostname : mail.company.ru ClientAuthenticationMethod : Ntlm IISAuthenticationMethods : {Ntlm} XropUrl : MetabasePath : IIS://CAS01.ad.company.ru/W3SVC/1/ROOT/Rpc Path : C:\Windows\System32\RpcProxy ExtendedProtectionTokenChecking : None ExtendedProtectionFlags : {} ExtendedProtectionSPNList : {} Server : CAS01 AdminDisplayName : ExchangeVersion : 0.10 (14.0.100.0) Name : Rpc (Default Web Site) DistinguishedName : CN=Rpc (Default Web Site),CN=HTTP,CN=Protocols,CN=CAS01,CN=Servers,CN=Exchange Admini strative Group (FYDIBOHF23SPDLT),CN=Administrative Groups,CN=First Organization,CN=Mi crosoft Exchange,CN=Services,CN=Configuration,DC=ad,DC=company,DC=ru Identity : CAS01\Rpc (Default Web Site) Guid : 408cebbe-db0b-4cb4-b7db-193f8c7aa1ec ObjectCategory : ad.company.ru/Configuration/Schema/ms-Exch-Rpc-Http-Virtual-Directory ObjectClass : {top, msExchVirtualDirectory, msExchRpcHttpVirtualDirectory} WhenChanged : 15.05.2012 15:33:30 WhenCreated : 15.05.2012 15:33:30 WhenChangedUTC : 15.05.2012 11:33:30 WhenCreatedUTC : 15.05.2012 11:33:30 OrganizationId : OriginatingServer : dc01.ad.company.ru IsValid : True Where from basic appears? It's even more interesting! I had this problem with CAS server with different name. I installed a new one (CAS01) uninstalled the first one. Assigned it to all databases. Server name in user Outlook profiles changed, but this problem is still there: switching between basic & ntlm :(