When working with Exchange 2010 and Outlook 2010 configurations, one particularly frustrating issue occurs when newly created AD users keep getting authentication prompts despite correct configuration. This behavior typically manifests immediately after mailbox creation.

• Prompt appears every Outlook launch
• Occurs primarily with new user accounts
• Standard solutions like unchecking "Always request authentication" don't work
• GPO updates don't resolve the issue

The root cause often lies in Active Directory replication delays and Outlook's cached credentials mechanism. Here's what's happening behind the scenes:

// Pseudo-code of the authentication flow
if (AD_Object_Not_Replicated || Outlook_Credential_Cache_Empty) {
    Show_Authentication_Prompt();
} else {
    Silent_Authentication();
}

1. Force AD Replication:

repadmin /syncall /A /e /q

2. Clear Outlook's credential cache:

rundll32.exe keymgr.dll, KRShowKeyMgr

3. Verify Autodiscover configuration:

Test-OutlookWebServices -Identity user@domain.com

For stubborn cases, modify the Windows registry (backup first!):

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\AutoDiscover]
"ExcludeExplicitO365Endpoint"=dword:00000001
"PreferLocalXML"=dword:00000001

• Implement proper AD site link costs for faster replication
• Configure Outlook profiles using PRF files for consistency
• Schedule regular GPO updates during off-hours

Use PowerShell to verify resolution:

Get-EventLog -LogName Application -Source "Outlook" -After (Get-Date).AddDays(-1) | 
Where {$_.EventID -eq 63} | 
Select-Object TimeGenerated,Message

When deploying new Active Directory users with Exchange 2010 mailboxes, some administrators encounter persistent credential prompts in Outlook 2010. This occurs despite:

• Correct Autodiscover configuration
• Proper Outlook profile setup
• Disabled "Always request authentication" option

The issue typically exhibits these characteristics:

1. Only affects newly created AD users
2. Occurs on first Outlook launch
3. Credential prompt reappears after reboot
4. gpupdate doesn't resolve the issue
5. Existing users work normally

Through troubleshooting multiple cases, I've identified these potential root causes:

1. Cached Credential Handshake Failure
Outlook fails to properly cache the authentication token due to permission inheritance delays in AD.

2. Autodiscover Cache Corruption
New profiles may create invalid registry entries under:
HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Autodiscover

Solution 1: Force Credential Rewrite

Run this PowerShell script on affected workstations:

# Clear existing Outlook credentials
cmdkey /delete:Microsoft_Office_16.0:Outlook /pass

# Recreate credential entry
$cred = Get-Credential
cmdkey /add:Microsoft_Office_16.0:Outlook /user:$cred.UserName /pass:$cred.GetNetworkCredential().Password

Solution 2: Registry Fix for Autodiscover

Create a batch file with these commands:

@echo off
reg delete "HKCU\Software\Microsoft\Office\14.0\Outlook\Autodiscover" /f
reg add "HKCU\Software\Microsoft\Office\14.0\Outlook\Autodiscover" /v "PreferLocalXML" /t REG_DWORD /d 0 /f

For environments where the above fails, check these Exchange components:

1. Ensure the Client Access Server has proper authentication methods:

   Get-OutlookAnywhere | Select Server,ExternalHostName,ExternalClientAuthenticationMethod

2. Verify EWS virtual directory settings:

   Get-WebServicesVirtualDirectory | Select Name,InternalAuthenticationMethods

To avoid this issue with future user creations:

• Run this AD replication check before mailbox creation:

  repadmin /syncall /AdeP

• Enable verbose logging in Outlook for new profiles:

  Outlook.exe /resetnavpane /cleanprofile /cleanautodiscover