# Outlook displays:
"Cannot start Microsoft Outlook. Cannot open the Outlook window.
The set of folders cannot be opened. The attempt to log on to
Microsoft Exchange has failed."

# Or:
"Microsoft Outlook cannot connect to Microsoft Exchange.
MAPI_E_NETWORK_ERROR 0x80040115"

# Or in Outlook status bar:
"Disconnected - MAPI_E_NETWORK_ERROR"

# Test basic connectivity
Test-NetConnection -ComputerName mail.domain.com -Port 443

# Test DNS resolution
Resolve-DnsName mail.domain.com
Resolve-DnsName autodiscover.domain.com

# Check for proxy settings
netsh winhttp show proxy

# Test HTTPS connectivity
Invoke-WebRequest -Uri "https://mail.domain.com/owa" -UseBasicParsing -TimeoutSec 10

# Verify Exchange services
Get-Service MSExchange* | Select-Object Name, Status | Format-Table

# Check IIS is running
Get-Service W3SVC | Select-Object Name, Status

# Test Outlook connectivity
Test-OutlookConnectivity -Protocol:HTTP -GetDefaultsFromAutodiscover:$true

# Check virtual directories
Get-OutlookAnywhere | Select-Object Server, ExternalHostname, InternalHostname

# On affected client, check Outlook connection status
# Hold Ctrl and right-click Outlook icon in system tray
# Select "Connection Status..."

# Check current connection type:
# - Outlook Anywhere (RPC/HTTP)
# - MAPI/HTTP
# - Direct RPC (internal only)

# Run Outlook diagnostics
outlook.exe /rpcdiag

# 1. Reset network adapter
ipconfig /release
ipconfig /renew
ipconfig /flushdns

# 2. Clear credential cache
# Control Panel > Credential Manager > Remove Exchange credentials

# 3. Test in Outlook Safe Mode
outlook.exe /safe

# 4. Create new Outlook profile
# Control Panel > Mail > Show Profiles > Add

# 5. Run Outlook repair
# Apps & Features > Microsoft Office > Modify > Online Repair

# Restart key Exchange services
Restart-Service MSExchangeRPC
Restart-Service MSExchangeServiceHost

# Recycle IIS application pools
Import-Module WebAdministration
Restart-WebAppPool -Name "MSExchangeRpcProxyAppPool"

# Reset IIS (more disruptive but comprehensive)
iisreset /noforce

# On client, verify DNS servers
Get-DnsClientServerAddress -AddressFamily IPv4

# Test DNS resolution
Resolve-DnsName mail.domain.com -Server 10.0.0.1  # Your DNS server

# If DNS fails, try public DNS temporarily
Set-DnsClientServerAddress -InterfaceAlias "Ethernet" -ServerAddresses "8.8.8.8"8.8.8","8.8.4.4"8.4.4"

# Check hosts file for conflicts
Get-Content C:\Windows\System32\drivers\etc\hosts | Select-String "mail|exchange"

# Clear DNS cache
Clear-DnsClientCache

# Check Windows Firewall
Get-NetFirewallRule -DisplayName "*Outlook*" | Select-Object DisplayName, Enabled, Direction, Action

# Temporarily disable firewall for testing (re-enable after!)
# Set-NetFirewallProfile -Profile Domain,Public,Private -Enabled False-Profile Domain,Public,Private -Enabled False

# Check proxy settings
Get-ItemProperty -Path "HKCU:\Software\Microsoft\Windows\CurrentVersion\Internet Settings" | Select-Object ProxyEnable, ProxyServer

# Bypass proxy for internal server (if applicable)
$bypassList = "*.domain.com;mail.domain.com;autodiscover.domain.com"
Set-ItemProperty -Path "HKCU:\Software\Microsoft\Windows\CurrentVersion\Internet Settings" -Name ProxyOverride -Value $bypassList

# Clear Windows credentials
cmdkey /list | Select-String "exchange|outlook|mail"
cmdkey /delete:mail.domain.com

# Clear Office credentials
# In Windows Credential Manager, remove entries under:
# - Windows Credentials
# - Generic Credentials
# Look for entries containing: MicrosoftOffice, Exchange, mail.domain.com

# Reset Outlook password prompt
# Delete this registry key to force re-authentication:
# HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Profiles\<ProfileName>\9375CFF0413111d3B88A00104B2A66760\Outlook\Profiles\<ProfileName>\9375CFF0413111d3B88A00104B2A6676

# Verify account is not locked
# On Domain Controller:
Get-ADUser -Identity username -Properties LockedOut, Enabled, PasswordExpired

# Check Outlook Anywhere settings
Get-OutlookAnywhere | Format-List Server, ExternalHostname, InternalHostname, ExternalClientsRequireSsl, IISAuthenticationMethods

# Check Autodiscover
Get-ClientAccessService | Select-Object Name, AutoDiscoverServiceInternalUri

# Verify virtual directories
Get-MapiVirtualDirectory | Select-Object Server, InternalUrl, ExternalUrl
Get-RpcProxyVirtualDirectory | Select-Object Server, InternalUrl, ExternalUrl

# Test Autodiscover
Test-OutlookWebServices -Identity admin@domain.com -TargetAddress admin@domain.com

# Test from client
$server = "mail.domain.com"
$port = 443

Write-Host "Testing connectivity to $server..."
$test = Test-NetConnection -ComputerName $server -Port $port

if ($test.TcpTestSucceeded) {
    Write-Host "TCP connection successful" -ForegroundColor Green

    # Test HTTPS
    try {
        $web = Invoke-WebRequest -Uri "https://$server/owa" -UseBasicParsing -TimeoutSec 10
        Write-Host "HTTPS connection successful (Status: $($web.StatusCode))" -ForegroundColor Green
    } catch {
        Write-Host "HTTPS failed: $($_.Exception.Message)" -ForegroundColor Red
    }
} else {
    Write-Host "TCP connection failed" -ForegroundColor Red
}

# Start Outlook and verify connection
Start-Process outlook.exe
Write-Host "Verify Outlook connects successfully"