What does HTTP 500 FolderSync mean in ActiveSync?

HTTP 500 during FolderSync indicates a server-side error when a mobile device attempts to synchronize its folder hierarchy with Exchange. The FolderSync command retrieves the list of available folders, and a 500 error means Exchange encountered an internal error processing this request.

Why do mobile devices fail to sync with Exchange?

Common causes include corrupted mailbox folder data, ActiveSync virtual directory misconfiguration, IIS application pool issues, certificate problems, mailbox database issues, or throttling policies blocking the sync.

How do I fix FolderSync failures for a single user?

First check if the issue is user-specific or server-wide. For single users, try removing and re-adding the Exchange account on the device, clearing the ActiveSync partnership, or running New-MailboxRepairRequest to fix mailbox corruption.

Can I test ActiveSync without a mobile device?

Yes, use the Microsoft Remote Connectivity Analyzer at testconnectivity.microsoft.com or run Test-ActiveSyncConnectivity cmdlet in Exchange Management Shell to test ActiveSync functionality without needing a physical device.

How do I enable detailed ActiveSync logging?

Enable ActiveSync logging via IIS or Set-EventLogLevel. Also enable mailbox logging for specific users with Set-CASMailbox -ActiveSyncDebugLogging $true. Logs are stored in the Exchange Logging folder under Sync.

What does HTTP 500 FolderSync mean in ActiveSync?

HTTP 500 during FolderSync indicates a server-side error when a mobile device attempts to synchronize its folder hierarchy with Exchange. The FolderSync command retrieves the list of available folders, and a 500 error means Exchange encountered an internal error processing this request.

Why do mobile devices fail to sync with Exchange?

Common causes include corrupted mailbox folder data, ActiveSync virtual directory misconfiguration, IIS application pool issues, certificate problems, mailbox database issues, or throttling policies blocking the sync.

How do I fix FolderSync failures for a single user?

First check if the issue is user-specific or server-wide. For single users, try removing and re-adding the Exchange account on the device, clearing the ActiveSync partnership, or running New-MailboxRepairRequest to fix mailbox corruption.

Can I test ActiveSync without a mobile device?

Yes, use the Microsoft Remote Connectivity Analyzer at testconnectivity.microsoft.com or run Test-ActiveSyncConnectivity cmdlet in Exchange Management Shell to test ActiveSync functionality without needing a physical device.

How do I enable detailed ActiveSync logging?

Enable ActiveSync logging via IIS or Set-EventLogLevel. Also enable mailbox logging for specific users with Set-CASMailbox -ActiveSyncDebugLogging $true. Logs are stored in the Exchange Logging folder under Sync.

HTTP 500: FolderSync Failed in ActiveSync

HTTP 500 FolderSync errors prevent mobile devices from synchronizing with Exchange Server, blocking access to email, calendar, and contacts on smartphones and tablets. This guide helps you diagnose and resolve ActiveSync sync failures.

Our ActiveSync Support Team specializes in mobile email troubleshooting and Exchange connectivity.

Error Overview: FolderSync Failures

The FolderSync command is one of the first ActiveSync commands a device sends to Exchange. It retrieves the folder hierarchy (Inbox, Sent Items, Calendar, etc.). When this fails with HTTP 500, the device cannot proceed with synchronization.

Typical Error Indicators

# IIS Log Entry (W3SVC logs)
2025-01-15 08:30:45 POST /Microsoft-Server-ActiveSync/default.eas
Cmd=FolderSync&User=john.doe&DeviceId=ABC123 443 - 10.0.0.50
Apple-iPhone/1234 500 0 0 1542

# Exchange ActiveSync Log
Cmd=FolderSync
User=john.doe@domain.com
Status=HTTP 500 Internal Server Error
Error=FolderSync failed with exception

# Device error message:
"Cannot verify account information.
Make sure your username and password are correct."

# Or on iOS:
"Unable to verify account information"

Symptoms & Business Impact

What Users Experience:

Mobile device shows "Cannot connect to server"
Account verification fails during setup
Email stops syncing on existing devices
Calendar and contacts not updating
Repeated password prompts on device

What Admins See:

HTTP 500 errors in IIS logs for ActiveSync
Event log errors from MSExchangeSync
Helpdesk tickets for mobile sync issues
Pattern may be single user or multiple users

Check ActiveSync Status

# Check ActiveSync virtual directory
Get-ActiveSyncVirtualDirectory | Select-Object Server, Name, InternalUrl, ExternalUrl, BasicAuthEnabled

# Check for recent sync errors
Get-EventLog -LogName Application -Source MSExchangeSync -Newest 20 | Where-Object { $_.EntryType -eq "Error" } | Format-List TimeGenerated, Message

# Test ActiveSync connectivity
Test-ActiveSyncConnectivity -ClientAccessServer EXCH01 | Format-List

Common Causes

1. Mailbox Corruption (30%)

Corrupted folder data in the user's mailbox prevents FolderSync from generating a valid response.

2. IIS/Application Pool Issues (25%)

The MSExchangeSyncAppPool is unhealthy, recycled during the request, or running with incorrect credentials.

3. Virtual Directory Misconfiguration (20%)

Incorrect URL settings, authentication configuration, or missing SSL bindings on the ActiveSync virtual directory.

4. Throttling Policy (15%)

User or device has hit ActiveSync throttling limits, causing the server to reject requests.

5. Device Partnership Issues (10%)

Corrupted device partnership data on the server requires clearing and re-establishing.

Quick Diagnosis

Step 1: Identify Scope

# Check if issue is single user or widespread
# Look at IIS logs for patterns
$logPath = "C:\inetpub\logs\LogFiles\W3SVC1"
$recentLog = Get-ChildItem $logPath -Filter "*.log" | Sort-Object LastWriteTime -Descending | Select-Object -First 1

# Search for 500 errors on ActiveSync
Get-Content $recentLog.FullName | Select-String "Microsoft-Server-ActiveSync.*500"-ActiveSync.*500" | Select-Object -Last 20

# Check affected users
Get-Content $recentLog.FullName | Select-String "Microsoft-Server-ActiveSync.*500"-ActiveSync.*500" | ForEach-Object {
    if ($_ -match "User=([^&]+)") { $matches[1] }
} | Group-Object | Sort-Object Count -Descending

Step 2: Check Virtual Directory

# Verify ActiveSync configuration
Get-ActiveSyncVirtualDirectory | Format-List Server, InternalUrl, ExternalUrl, BasicAuthEnabled, WindowsAuthEnabled, ClientCertAuth

# Check IIS binding
Import-Module WebAdministration
Get-WebBinding -Name "Default Web Site" | Format-Table Protocol, bindingInformation

# Verify application pool
Get-WebAppPoolState -Name "MSExchangeSyncAppPool"
Get-ItemProperty "IIS:\AppPools\MSExchangeSyncAppPool" | Select-Object Name, State, autoStart

Step 3: Test User's Mailbox

# Test ActiveSync for specific user
$user = "john.doe@domain.com"
$cred = Get-Credential -UserName $user -Message "Enter user password"
Test-ActiveSyncConnectivity -TargetEmailAddress $user -Credentials $cred

# Check user's ActiveSync devices
Get-ActiveSyncDeviceStatistics -Mailbox $user | Select-Object DeviceId, DeviceType, LastSuccessSync, Status

# Check for mailbox issues
Get-MailboxStatistics -Identity $user | Select-Object DisplayName, TotalItemSize, ItemCount, DatabaseName

Quick Fixes

Recycle ActiveSync Application Pool

# Recycle the application pool (minimal impact)
Import-Module WebAdministration
Restart-WebAppPool -Name "MSExchangeSyncAppPool"

# Wait for pool to restart
Start-Sleep -Seconds 10

# Verify pool is running
Get-WebAppPoolState -Name "MSExchangeSyncAppPool"

Write-Host "Application pool recycled. Have user retry sync."

Clear User's Device Partnership

# List user's ActiveSync devices
$user = "john.doe@domain.com"
Get-ActiveSyncDeviceStatistics -Mailbox $user | Format-Table DeviceId, DeviceType, FirstSyncTime, LastSuccessSync

# Remove problematic device partnership
$deviceId = "ABC123"  # Get from above
Remove-ActiveSyncDevice -Identity "$user\$deviceId"$deviceId" -Confirm:$false

# User should now re-add account on device

Detailed Solutions

Solution 1: Repair User Mailbox

Fix Mailbox Folder Corruption

# Run mailbox repair for folder view issues
$user = "john.doe@domain.com"
New-MailboxRepairRequest -Mailbox $user -CorruptionType FolderView -DetectOnly

# If issues found, run repair
New-MailboxRepairRequest -Mailbox $user -CorruptionType FolderView, ProvisionedFolder, SearchFolder

# Check repair status
Get-MailboxRepairRequest -Mailbox $user | Format-List

# Alternative: Move mailbox to new database (repairs during move)
# New-MoveRequest -Identity $user -TargetDatabase "NewMailboxDB"-Identity $user -TargetDatabase "NewMailboxDB"

Solution 2: Fix Virtual Directory

Recreate ActiveSync Virtual Directory

# Remove and recreate if corrupted
$server = $env:COMPUTERNAME

# Get current settings first
$current = Get-ActiveSyncVirtualDirectory -Server $server
$current | Export-Clixml "C:\Temp\ActiveSync_Backup.xml"

# Remove existing
Remove-ActiveSyncVirtualDirectory -Identity "$server\Microsoft-Server-ActiveSync (Default Web Site)"-Server-ActiveSync (Default Web Site)" -Confirm:$false

# Create new with correct settings
New-ActiveSyncVirtualDirectory -Server $server -WebSiteName "Default Web Site" -InternalUrl "https://mail.domain.com/Microsoft-Server-ActiveSync"-ActiveSync" -ExternalUrl "https://mail.domain.com/Microsoft-Server-ActiveSync"-ActiveSync"

# Restart IIS
iisreset /noforce

Solution 3: Check Throttling Policy

Review and Adjust Throttling

# Check user's throttling policy
$user = "john.doe@domain.com"
$mailbox = Get-Mailbox -Identity $user
$policy = Get-ThrottlingPolicy -Identity $mailbox.ThrottlingPolicy

# Check ActiveSync-related limits
$policy | Select-Object Name, EasMaxDevices, EasMaxConcurrency, EasMaxDeviceDeletesPerMonth

# If limits are too restrictive, create custom policy
New-ThrottlingPolicy -Name "ActiveSyncRelaxed" -EasMaxDevices 20 -EasMaxConcurrency 10 -EasMaxDeviceDeletesPerMonth 30

# Apply to user
Set-Mailbox -Identity $user -ThrottlingPolicy "ActiveSyncRelaxed"

# Or use default policy with higher limits
Set-ThrottlingPolicy -Identity GlobalThrottlingPolicy_<GUID> -EasMaxDevices 15

Solution 4: Enable Debug Logging

Enable ActiveSync Debug Logging

# Enable mailbox-level debug logging
$user = "john.doe@domain.com"
Set-CASMailbox -Identity $user -ActiveSyncDebugLogging $true

# Have user attempt sync, then check logs
$logPath = "$env:ExchangeInstallPath\Logging\Sync\Troubleshooter"
Get-ChildItem $logPath -Recurse | Where-Object { $_.LastWriteTime -gt (Get-Date).AddHours(-1) }

# Read recent log file
$recentLog = Get-ChildItem $logPath -Recurse | Sort-Object LastWriteTime -Descending | Select-Object -First 1
Get-Content $recentLog.FullName | Select-Object -Last 100

# Disable logging when done (it impacts performance)
Set-CASMailbox -Identity $user -ActiveSyncDebugLogging $false

Verify the Fix

Test ActiveSync Connectivity

# Use Remote Connectivity Analyzer (online)
Write-Host "Test at: https://testconnectivity.microsoft.com"
Write-Host "Select: Exchange ActiveSync"
Write-Host ""

# Or test via PowerShell
$user = "john.doe@domain.com"
$cred = Get-Credential -UserName $user -Message "Enter password"
$result = Test-ActiveSyncConnectivity -TargetEmailAddress $user -Credentials $cred

$result | Format-List Scenario, Result, Latency, Error

# Check IIS logs for successful syncs
$logPath = "C:\inetpub\logs\LogFiles\W3SVC1"
$recentLog = Get-ChildItem $logPath -Filter "*.log" | Sort-Object LastWriteTime -Descending | Select-Object -First 1
Get-Content $recentLog.FullName | Select-String "Microsoft-Server-ActiveSync.*$($user -replace '@','%40').*200"-ActiveSync.*$($user -replace '@','%40').*200" | Select-Object -Last 5

Prevention Tips

Best Practices

Monitor ActiveSync health with synthetic tests
Set appropriate device limits in throttling policies
Keep application pools healthy with scheduled recycling
Maintain valid SSL certificates for ActiveSync
Document supported device types and configurations
Use Mobile Device Mailbox Policy for security

When to Escalate

Contact Exchange specialists if:

Multiple users affected with same error
Virtual directory recreation doesn't help
Mailbox repair shows persistent corruption
Load balancer or proxy involvement
Need certificate or authentication troubleshooting

Need Expert Help?

Our ActiveSync Support Team provides comprehensive mobile sync troubleshooting and Exchange connectivity optimization.