HTTP 404 Not Found: OWA/ECP Missing Files - Fix Guide 2025

# Browser shows:
HTTP Error 404.0 - Not Found
The resource you are looking for has been removed, had its name changed,
or is temporarily unavailable.

# IIS Log entry:
2025-01-15 10:45:22 W3SVC1 GET /owa/ - 443 - 192.168.1.100 Mozilla/5.0 - 404 0 2 125

# Common 404 sub-status codes:-status codes:
# 404.0 - File or directory not found0 - File or directory not found
# 404.2 - ISAPI or CGI restriction2 - ISAPI or CGI restriction
# 404.3 - MIME type restriction3 - MIME type restriction
# 404.4 - No handler configured4 - No handler configured
# 404.7 - File extension denied7 - File extension denied
# 404.8 - Hidden namespace8 - Hidden namespace

Import-Module WebAdministration

# Check if app already exists
$existing = Get-WebApplication -Site "Default Web Site" -Name "owa" -ErrorAction SilentlyContinue

if ($existing) {
    Write-Host "OWA already exists in IIS - skipping creation"
} else {
    # Create the virtual application
    $physicalPath = "$env:ExchangeInstallPath\ClientAccess\Owa"

    if (Test-Path $physicalPath) {
        New-WebApplication -Site "Default Web Site" -Name "owa" -PhysicalPath $physicalPath -ApplicationPool "MSExchangeOWAAppPool"

        Write-Host "OWA virtual application created" -ForegroundColor Green
    } else {
        Write-Host "ERROR: Physical path doesn't exist: $physicalPath" -ForegroundColor Red
        Write-Host "Files may need to be restored - see detailed solutions"
    }
}

# Verify
Get-WebApplication -Site "Default Web Site" -Name "owa"

# Restart OWA app pool
Import-Module WebAdministration
Restart-WebAppPool -Name "MSExchangeOWAAppPool"
Write-Host "OWA app pool recycled"

# Full IIS reset if needed
iisreset /noforce

# Wait and test
Start-Sleep -Seconds 15

try {
    $response = Invoke-WebRequest -Uri "https://localhost/owa/" -UseBasicParsing -TimeoutSec 30
    Write-Host "OWA Status: $($response.StatusCode)" -ForegroundColor Green
} catch {
    Write-Host "OWA Error: $($_.Exception.Response.StatusCode)" -ForegroundColor Red
}

Import-Module WebAdministration

$correctPath = "$env:ExchangeInstallPath\ClientAccess\Owa"

# Update physical path
Set-ItemProperty "IIS:\Sites\Default Web Site\owa" -Name physicalPath -Value $correctPath

# Verify
$newPath = (Get-WebApplication -Site "Default Web Site" -Name "owa").PhysicalPath
Write-Host "Physical path updated to: $newPath"

# Test file existence
if (Test-Path "$newPath\web.config") {
    Write-Host "web.config found - path correct" -ForegroundColor Green
} else {
    Write-Host "web.config missing - files may need restoration" -ForegroundColor Red
}

# Option 1: Rerun the Cumulative Update
# This will restore missing files

# Find the CU installer
$cuPath = "D:\ExchangeUpdates\ExchangeServer2019-CU14.exe"  # Adjust path

# Run in repair/upgrade mode
& $cuPath /mode:upgrade /IAcceptExchangeServerLicenseTerms

# This process takes 30-60 minutes and restores all files-60 minutes and restores all files

# Option 2: Extract and copy files manually
# Extract CU without installing
# & $cuPath /extract:D:\ExchangeExtract

# Then copy missing files from extracted location to:
# $env:ExchangeInstallPath\ClientAccess\Owa

# Common AV quarantine locations (vary by product)
$quarantinePaths = @(
    "C:\ProgramData\Microsoft\Windows Defender\Quarantine",
    "C:\ProgramData\Symantec\Quarantine",
    "C:\Quarantine"
)

foreach ($path in $quarantinePaths) {
    if (Test-Path $path) {
        Write-Host "Checking: $path" -ForegroundColor Cyan
        $files = Get-ChildItem $path -Recurse -ErrorAction SilentlyContinue
        if ($files) {
            Write-Host "  Found $($files.Count) quarantined items"
        }
    }
}

# Add Exchange exclusions to Windows Defender
$excludePaths = @(
    "$env:ExchangeInstallPath",
    "$env:ExchangeInstallPath\ClientAccess",
    "$env:SystemDrive\inetpub\temp\IIS Temporary Compressed Files"
)

foreach ($path in $excludePaths) {
    Add-MpPreference -ExclusionPath $path
    Write-Host "Added exclusion: $path"
}

# For other AV products, consult their documentation for:
# 1. Viewing quarantine
# 2. Restoring files
# 3. Adding exclusions

# Step 1: Remove existing (broken) virtual directory
Get-OwaVirtualDirectory -Server $env:COMPUTERNAME | Remove-OwaVirtualDirectory -Confirm:$false

# Also remove from IIS if still present
Import-Module WebAdministration
$iisOwa = Get-WebApplication -Site "Default Web Site" -Name "owa" -ErrorAction SilentlyContinue
if ($iisOwa) {
    Remove-WebApplication -Site "Default Web Site" -Name "owa"
    Write-Host "Removed OWA from IIS"
}

# Step 2: Verify physical files exist
$owaPath = "$env:ExchangeInstallPath\ClientAccess\Owa"
if (-not (Test-Path "$owaPath\web.config")) {
    Write-Host "ERROR: OWA files missing - run Exchange setup /mode:upgrade first" -ForegroundColor Red
    return
}

# Step 3: Create new virtual directory
New-OwaVirtualDirectory -Server $env:COMPUTERNAME -WebSiteName "Default Web Site"

# Step 4: Configure URLs
$internalUrl = "https://mail.company.com/owa"
$externalUrl = "https://mail.company.com/owa"

Get-OwaVirtualDirectory -Server $env:COMPUTERNAME |
  Set-OwaVirtualDirectory -InternalUrl $internalUrl -ExternalUrl $externalUrl

# Step 5: Configure authentication
Get-OwaVirtualDirectory -Server $env:COMPUTERNAME |
  Set-OwaVirtualDirectory -FormsAuthentication $true

# Step 6: Reset IIS
iisreset /noforce

Write-Host "OWA virtual directory recreated" -ForegroundColor Green

# Re-register ASP.NET with IIS
$frameworkPath = "$env:windir\Microsoft.NET\Framework64\v4.0.30319"0.30319"

& "$frameworkPath\aspnet_regiis.exe" -i

# Verify .NET is registered
Write-Host "Checking ASP.NET registration..."
& "$frameworkPath\aspnet_regiis.exe" -lv

# Check handler mappings exist
Import-Module WebAdministration

$handlers = Get-WebHandler -PSPath "IIS:\Sites\Default Web Site\owa" |
  Where-Object {$_.Path -like "*.aspx"}

if ($handlers) {
    Write-Host ".aspx handlers configured:" -ForegroundColor Green
    $handlers | Select-Object Name, Path | Format-Table
} else {
    Write-Host "No .aspx handlers - running repair..." -ForegroundColor Yellow

    # This typically requires full IIS feature reinstall or Exchange setup repair
    Write-Host "Run: Exchange setup /mode:upgrade"
}

# Reset IIS
iisreset /noforce

# 1. Test OWA URL directly
$urls = @(
    "https://localhost/owa/",
    "https://localhost/owa/auth/logon.aspx",
    "https://localhost/ecp/"
)

foreach ($url in $urls) {
    try {
        $response = Invoke-WebRequest -Uri $url -UseBasicParsing -TimeoutSec 15
        Write-Host "$url - $($response.StatusCode)"$response.StatusCode)" -ForegroundColor Green
    } catch {
        $status = $_.Exception.Response.StatusCode.value__
        Write-Host "$url - $status"$status" -ForegroundColor Red
    }
}

# 2. Full connectivity test
Test-OwaConnectivity | Select-Object Scenario, Result, Latency | Format-Table

# 3. Verify virtual directory configuration
Get-OwaVirtualDirectory | Select-Object Server, InternalUrl, ExternalUrl

# 4. Check IIS status
Import-Module WebAdministration
Get-WebApplication -Site "Default Web Site" | Where-Object {$_.Path -match "owa|ecp"} |
  Select-Object Path, PhysicalPath, ApplicationPool

# 5. Check no new 404 errors404 errors
$logPath = "$env:SystemDrive\inetpub\logs\LogFiles\W3SVC1"
$latestLog = Get-ChildItem $logPath -Filter "*.log" | Sort-Object LastWriteTime -Descending | Select-Object -First 1
$recent404 = Get-Content $latestLog.FullName | Select-Object -Last 100 |
  Where-Object {$_ -match "/owa" -and $_ -match " 404 "}
Write-Host "Recent OWA 404s: $($recent404.Count)"

# Add Exchange exclusions to Windows Defender
$exclusions = @(
    "$env:ExchangeInstallPath",
    "$env:ExchangeInstallPath\Logging",
    "$env:ExchangeInstallPath\TransportRoles\data",
    "$env:ExchangeInstallPath\Mailbox\MDBTEMP",
    "$env:SystemDrive\inetpub\temp\IIS Temporary Compressed Files",
    "$env:SystemRoot\System32\inetsrv"
)

foreach ($path in $exclusions) {
    Add-MpPreference -ExclusionPath $path
    Write-Host "Excluded: $path"
}

# Also exclude processes
$processes = @(
    "EdgeTransport.exe",
    "w3wp.exe",
    "Microsoft.Exchange.*.exe"
)

foreach ($proc in $processes) {
    Add-MpPreference -ExclusionProcess $proc
}

Write-Host "`nRemember to configure exclusions in third-party AV as well!"

# Run after every Cumulative Update
Write-Host "Post-CU Virtual Directory Check" -ForegroundColor Cyan

$vdirs = @(
    @{Name="OWA"; Get="Get-OwaVirtualDirectory"; Path="/owa"},
    @{Name="ECP"; Get="Get-EcpVirtualDirectory"; Path="/ecp"},
    @{Name="EWS"; Get="Get-WebServicesVirtualDirectory"; Path="/ews"},
    @{Name="OAB"; Get="Get-OabVirtualDirectory"; Path="/oab"}
)

foreach ($vdir in $vdirs) {
    # Check Exchange
    $exResult = Invoke-Expression "$($vdir.Get) -Server $env:COMPUTERNAME"-Server $env:COMPUTERNAME"
    $exStatus = if($exResult){"OK"}else{"MISSING"}

    # Check IIS
    Import-Module WebAdministration
    $iisResult = Get-WebApplication -Site "Default Web Site" -Name $vdir.Path.TrimStart('/') -ErrorAction SilentlyContinue
    $iisStatus = if($iisResult){"OK"}else{"MISSING"}

    Write-Host "$($vdir.Name): Exchange=$exStatus, IIS=$iisStatus"$exStatus, IIS=$iisStatus"
}

# Quick URL test
Test-OwaConnectivity -ClientAccessServer $env:COMPUTERNAME |
  Select-Object Scenario, Result | Format-Table