Exchange Server 2019 ECP and OWA fail to load with 500 error

Hello Erin Cruz

Thank you for reaching out to Microsoft Support and providing details about the issue on your Exchange Server 2019. There have been similar reported cases about the "500 Unexpected" Error, this could stem from configuration issues, corrupted files, unhealthy mailboxes, or post-update assembly problems. Here something you can try to resolve this:

If the admin account lacks a mailbox or arbitration mailboxes are unhealthy, Exchange can't properly proxy the post-login request, leading to a 500 error.

• Run: Enable-Mailbox -Identity <your-admin-username> This creates a mailbox if missing.
• Check arbitration mailboxes: Get-Mailbox -Arbitration. You should see 7 healthy mailboxes with no errors. If any are missing or corrupted, recreate them by following Microsoft's guide.

Stopped/failed services can trigger this, please check and restart Exchange Services .

• List services: Get-Service | Where {$_.DisplayName -Like "*Exchange*"} | Format-Table DisplayName, Name, Status.
• Start any stopped ones: Start-Service <ServiceName> (like Start-Service MSExchangeFrontendTransport).

Corrupted XAML or config files often cause ASP.NET warnings and 500 errors. In this case you need to inspect and repair configuration files

• Navigate to C:\Program Files\Microsoft\Exchange Server\V15\Bin in EMS.
• Run: .\UpdateConfigFiles.ps1 followed by .\UpdateCAS.ps1. These refresh Client Access Server configs and may take a few minutes.
• If Event Viewer mentions a FileNotFoundException for 'Microsoft.Exchange.ManagementGUI' or XAML parse errors (involving RemoteDomains.XAML), replace C:\Program Files\Microsoft\Exchange Server\V15\ClientAccess\ecp\DDI\RemoteDomains.XAML with a copy from your Exchange setup media or a working server of the same version. Then run iisreset.

You can also try to recreate ECP and OWA Virtual Directories. This rebuilds the web interfaces if they're corrupted (common after updates or config changes). Backup your current IIS settings first via IIS Manager export.

• Remove ECP: Remove-EcpVirtualDirectory -Identity "<ServerName>\ecp (Default Web Site)".
• Recreate ECP: New-EcpVirtualDirectory -Server <ServerName> -ExternalUrl https://<your-external-url>/ecp -InternalUrl https://<your-internal-url>/ecp.
• Remove OWA: Remove-OwaVirtualDirectory -Identity "<ServerName>\owa (Default Web Site)".
• Recreate OWA: New-OwaVirtualDirectory -Server <ServerName> -ExternalUrl https://<your-external-url>/owa -InternalUrl https://<your-internal-url>/owa.
• Run iisreset and test. Note: This may change the login to a pop-up form.

If none of these do the trick, please comment bellow with the exact Event Viewer error details. I will support you further.

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