How to Fix EWS Connection Issues in Acronis Cyber Protect for Microsoft 365 Backups

by | Apr 8, 2025 | Uncategorized

acronis cyber protect office 365

When configuring Microsoft 365 backups in Acronis Cyber Protect Advanced, you may encounter the following error message:

Failed to connect to the Exchange server 'https://outlook.office365.com/EWS/Exchange.asmx' using EWS APIError code: 5963824.NET exception 'System.Net.WebException': The underlying connection was closed: An unexpected error occurred on a receive.

Table of Contents

Root Cause

This error typically indicates a failure in establishing a secure TLS connection between Acronis and Microsoft Exchange Online. It may be caused by:

  • Outdated .NET/TLS settings on the server
  • Missing Azure AD permissions or expired app registration
  • Firewall or proxy interference
  • Obsolete Acronis agent components

Step-by-Step Fix

1. Ensure TLS 1.2 is Enabled

Apply the following registry keys:

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\v4.0.30319]"SchUseStrongCrypto"=dword:00000001"SystemDefaultTlsVersions"=dword:00000001[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\.NETFramework\v4.0.30319]"SchUseStrongCrypto"=dword:00000001"SystemDefaultTlsVersions"=dword:00000001

Then reboot the system.

2. Test the EWS Connection

PowerShell:Invoke-WebRequest https://outlook.office365.com/EWS/Exchange.asmx

The request should return an HTTP status (401 Unauthorized is fine – it proves connectivity).

3. Verify Azure App Registration

  • Ensure the app is registered in Azure AD
  • Grant full_access_as_app permissions for Exchange
  • Consent as an administrator in the Azure portal

4. Reauthorize Microsoft 365 in Acronis

In the Acronis web console:

  • Remove and re-add the Microsoft 365 account
  • This forces token refresh and reinitializes the connection

5. Update Acronis

Ensure you’re running the latest version of Acronis Cyber Protect Advanced, as older versions (pre-15.0.29280) have known TLS/EWS issues.

6. Check Firewall / Proxy

Allow direct access to the following domains:

  • outlook.office365.com
  • login.microsoftonline.com
  • graph.microsoft.com

If TLS inspection is enabled, add exceptions for Acronis traffic or disable inspection for outbound Microsoft 365 traffic.

Conclusion

By enabling TLS 1.2, validating Azure permissions, and verifying connectivity, you can resolve the EWS API connection issue and ensure seamless backups of Microsoft 365 mailboxes using Acronis Cyber Protect.