Event ID 4999: OWA Application Crash - Fix Guide 2025

Log Name:      Application
Source:        MSExchange Common
Event ID:      4999
Level:         Error
Description:   Watson report about to be sent for process id: 12456,
               with parameters: E12, c-RTL-AMD64, 15.02.1118.026,
               w3wp#MSExchangeOWAAppPool, M.Exchange.Clients.Owa2.Server,
               M.E.C.O.S.Core.OwaApplication.HandleUnhandledException,
               System.OutOfMemoryException, 7948, 15.02.1118.026.
               ErrorReportingEnabled: False

# Import IIS module
Import-Module WebAdministration

# Restart OWA app pool
Restart-WebAppPool -Name "MSExchangeOWAAppPool"

# Verify it started
Start-Sleep -Seconds 5
Get-WebAppPoolState -Name "MSExchangeOWAAppPool"

# If still stopped, force start
Start-WebAppPool -Name "MSExchangeOWAAppPool"

# Also restart ECP if needed
Restart-WebAppPool -Name "MSExchangeECPAppPool"

# Check if Rapid Fail Protection triggered
Get-WinEvent -FilterHashtable @{
    LogName = 'System'
    ProviderName = 'WAS'
    Id = 5002
} -MaxEvents 5 -ErrorAction SilentlyContinue

# Temporarily disable Rapid Fail Protection
Import-Module WebAdministration
Set-ItemProperty IIS:\AppPools\MSExchangeOWAAppPool -Name failure.rapidFailProtection -Value $false

# Start the app pool
Start-WebAppPool -Name "MSExchangeOWAAppPool"

# Re-enable after fixing root cause
# Set-ItemProperty IIS:\AppPools\MSExchangeOWAAppPool -Name failure.rapidFailProtection -Value $true-Name failure.rapidFailProtection -Value $true

# Recycle all IIS app pools (cleaner than full restart)
& "$env:windir\system32\inetsrv\appcmd.exe" recycle apppool /apppool.name:"MSExchangeOWAAppPool"
& "$env:windir\system32\inetsrv\appcmd.exe" recycle apppool /apppool.name:"MSExchangeECPAppPool"
& "$env:windir\system32\inetsrv\appcmd.exe" recycle apppool /apppool.name:"MSExchangeServicesAppPool"

# If crashes persist, full IIS reset
iisreset /noforce

# Nuclear option: Restart all Exchange services
Get-Service *Exchange* | Where-Object {$_.Status -eq 'Running'} | Restart-Service -Force

Import-Module WebAdministration

# Set private memory limit (recycle when exceeded) - in KB
# Example: 4GB = 4194304 KB
Set-ItemProperty IIS:\AppPools\MSExchangeOWAAppPool -Name recycling.periodicRestart.privateMemory -Value 4194304

# Set virtual memory limit
Set-ItemProperty IIS:\AppPools\MSExchangeOWAAppPool -Name recycling.periodicRestart.memory -Value 8388608

# Configure scheduled recycling (off-peak: 3 AM)3 AM)
Clear-ItemProperty IIS:\AppPools\MSExchangeOWAAppPool -Name recycling.periodicRestart.schedule
Set-ItemProperty IIS:\AppPools\MSExchangeOWAAppPool -Name recycling.periodicRestart.schedule -Value @{value="03:00:00"00:00"}

# Verify settings
Get-ItemProperty IIS:\AppPools\MSExchangeOWAAppPool -Name recycling | Select-Object -ExpandProperty periodicRestart

# Check current memory allocation
Get-Process w3wp | Measure-Object WorkingSet64 -Sum |
  Select-Object @{N='TotalIISMemoryGB';E={[math]::Round($_.Sum/1GB,2)}}

# For memory leaks, enable 32-bit mode if not critical for capacity-bit mode if not critical for capacity
# WARNING: Limits each worker to ~3GB but can help with certain leaks
# Set-ItemProperty IIS:\AppPools\MSExchangeOWAAppPool -Name enable32BitAppOnWin64 -Value $true-Name enable32BitAppOnWin64 -Value $true

# Better: Add more physical RAM to server
# Recommended: 32GB+ for 500+ mailbox deployments

# Enable GC Server mode for better memory management
# Add to OWA web.config:
# <runtime><gcServer enabled="true"/></runtime>

# Get current Exchange build number
$build = (Get-ExchangeServer).AdminDisplayVersion
Write-Host "Current build: $build"

# Check Microsoft's build number page for latest CU
# https://docs.microsoft.com/exchange/new-features/build-numbers-and-release-dates

# Before installing CU, check prerequisites
# 1. Backup all databases
Get-MailboxDatabase | ForEach-Object {
    Write-Host "Database: $($_.Name) - Path: $($_.EdbFilePath)"
}

# 2. Check disk space for CU installation
Get-PSDrive C | Select-Object @{N='FreeGB';E={[math]::Round($_.Free/1GB,2)}}

# 3. Put server in maintenance mode if in DAG
# Set-ServerComponentState $env:COMPUTERNAME -Component ServerWideOffline -State Inactive -Requester Maintenance$env:COMPUTERNAME -Component ServerWideOffline -State Inactive -Requester Maintenance

# Check .NET Framework versions installed
Get-ChildItem 'HKLM:\SOFTWARE\Microsoft\NET Framework Setup\NDP' -Recurse |
  Get-ItemProperty -Name Version -ErrorAction SilentlyContinue |
  Where-Object {$_.Version -match '^\d'} |
  Select-Object PSChildName, Version

# Clear .NET temporary assemblies
Remove-Item "$env:windir\Microsoft.NET\Framework64\v4.0.30319\Temporary ASP.NET Files\*"0.30319\Temporary ASP.NET Files\*" -Recurse -Force -ErrorAction SilentlyContinue

# Reset IIS to regenerate assemblies
iisreset

# If still failing, run .NET repair tool
# Download from: https://www.microsoft.com/download/details.aspx?id=30135

# Alternatively, reinstall ASP.NET
# & "$env:windir\Microsoft.NET\Framework64\v4.0.30319\aspnet_regiis.exe" -i0.30319\aspnet_regiis.exe" -i

# Check for OWA customizations
$owaPath = "$env:ExchangeInstallPath\ClientAccess\Owa"
Get-ChildItem "$owaPath\prem" -Recurse -Filter "*.dll" |
  Where-Object {$_.VersionInfo.CompanyName -notlike "*Microsoft*"} |
  Select-Object Name, @{N='Company';E={$_.VersionInfo.CompanyName}}, FullName

# Check web.config for third-party modules
$webConfig = Get-Content "$owaPath\web.config" -Raw
if ($webConfig -match "httpModules|httpHandlers") {
    Write-Host "Custom HTTP modules found - review web.config"
}

# Backup and reset OWA virtual directory if heavily customized
# WARNING: This removes customizations
# Get-OwaVirtualDirectory | Remove-OwaVirtualDirectoryRemove-OwaVirtualDirectory
# New-OwaVirtualDirectory -Server $env:COMPUTERNAME-Server $env:COMPUTERNAME

# Check mailbox database status
Get-MailboxDatabase -Status | Select-Object Name, Server, Mounted, DatabaseSize

# Test OWA to backend connectivity
Test-OwaConnectivity -ClientAccessServer $env:COMPUTERNAME |
  Format-List Scenario, Result, Latency, Error

# Check RPC connectivity
Get-RpcClientAccess | Select-Object Server, Responsibility

# Verify backend services
Get-Service MSExchangeIS, MSExchangeRPC | Select-Object Name, Status

# Restart Information Store if needed
Restart-Service MSExchangeIS -Force

# 1. Check app pool is running and stable
Import-Module WebAdministration
Get-IISAppPool | Where-Object {$_.Name -like "*Exchange*"} |
  Select-Object Name, State

# 2. Test OWA connectivity
$testUser = "administrator@domain.com"
Test-OwaConnectivity -URL "https://mail.domain.com/owa" |
  Select-Object Scenario, Result, Latency

# 3. Monitor for new crashes (wait 30 minutes)30 minutes)
$startTime = (Get-Date).AddMinutes(-30)
Get-WinEvent -FilterHashtable @{
    LogName = 'Application'
    ProviderName = 'MSExchange Common'
    Id = 4999
    StartTime = $startTime
} -ErrorAction SilentlyContinue | Measure-Object

# 4. Check memory is stable
Get-Process w3wp | Where-Object {
    (Get-CimInstance Win32_Process -Filter "ProcessId=$($_.Id)").CommandLine -like "*OWA*"
} | Select-Object Id, @{N='MemoryMB';E={[math]::Round($_.WorkingSet64/1MB,2)}}

# 5. Verify no new Watson dumps
$watsonPath = "$env:ExchangeInstallPath\Logging\Diagnostics\Watson"
Get-ChildItem $watsonPath -Recurse -Filter "*.dmp" |
  Where-Object {$_.LastWriteTime -gt $startTime} | Measure-Object

# Check current vs latest CU
$current = (Get-ExchangeServer).AdminDisplayVersion
Write-Host "Current: $current"
Write-Host "Check latest at: https://docs.microsoft.com/exchange/new-features/build-numbers-and-release-dates"-numbers-and-release-dates"

# Create scheduled task to check for updates monthly
$action = New-ScheduledTaskAction -Execute "PowerShell.exe" -Argument @"
-NoProfile -Command "-Command "
  Add-PSSnapin Microsoft.Exchange.Management.PowerShell.SnapIn
  $ver = (Get-ExchangeServer).AdminDisplayVersion
  Send-MailMessage -To 'admin@domain.com' -From 'exchange@domain.com' -Subject 'Exchange Version Check' -Body $ver -SmtpServer localhost
"
"@
Register-ScheduledTask -TaskName "Exchange-Version-Check"-Check" -Action $action -Trigger (New-ScheduledTaskTrigger -Weekly -At 9am -DaysOfWeek Monday)

Import-Module WebAdministration

# Configure optimal recycling for OWA
$appPool = "MSExchangeOWAAppPool"

# Recycle at 3 AM daily
Set-ItemProperty "IIS:\AppPools\$appPool" -Name recycling.periodicRestart.schedule -Value @{value="03:00:00"00:00"}

# Recycle when memory exceeds 4GB
Set-ItemProperty "IIS:\AppPools\$appPool" -Name recycling.periodicRestart.privateMemory -Value 4194304

# Enable overlap recycling (no downtime during recycle)
Set-ItemProperty "IIS:\AppPools\$appPool" -Name recycling.disallowOverlappingRotation -Value $false

# Log recycling events
Set-ItemProperty "IIS:\AppPools\$appPool" -Name recycling.logEventOnRecycle -Value "Time,Memory,Schedule,Requests,ConfigChange"

# Save as Check-OWAHealth.ps1 and schedule hourly
$threshold = 3500 # MB

$owaProcess = Get-Process w3wp -ErrorAction SilentlyContinue | Where-Object {
    (Get-CimInstance Win32_Process -Filter "ProcessId=$($_.Id)").CommandLine -like "*OWA*"
}

if ($owaProcess) {
    $memoryMB = [math]::Round($owaProcess.WorkingSet64/1MB, 2)

    if ($memoryMB -gt $threshold) {
        $body = "OWA memory usage: $memoryMB MB (threshold: $threshold MB)"$threshold MB)"
        $body += "`nConsider recycling app pool or investigating memory leak"

        Send-MailMessage -To "admin@domain.com" -From "monitor@domain.com" -Subject "WARNING: OWA High Memory" -Body $body -SmtpServer localhost
    }
}