You open Outlook, click the ndMail panel, and get "Unable to retrieve session data" or a login screen that loops endlessly. The ndMail add-in cannot authenticate to NetDocuments, so email filing stops working. This is one of the most common NetDocs issues in legal environments, and the fix usually comes down to cached credentials, a wrong host registry key, or a browser cookie problem.

What Causes ndMail Login Failures

The ndMail add-in authenticates to NetDocuments using OAuth through an embedded browser component. When any part of that authentication chain breaks, you get login loops or session errors.

Common causes:

  • Stale OAuth tokens. The cached token expired or was invalidated by a password change, MFA reset, or admin policy update.
  • Wrong Host registry value. NetDocuments has multiple regional data centers. If the Host registry key points to the wrong region, authentication fails silently.
  • Browser cache and cookies. The embedded browser stores cookies that can become corrupt or stale after updates.
  • Proxy or firewall blocking. Corporate firewalls that inspect HTTPS traffic can interfere with the OAuth flow to NetDocuments servers.
  • ndMail version mismatch. An outdated ndMail version may use deprecated authentication endpoints.

Fix 1: Clear NetDocuments Cached Credentials

The fastest fix. Remove stored credentials so ndMail is forced to re-authenticate.

  1. Close Outlook completely.
  2. Open Control Panel > Credential Manager > Generic Credentials.
  3. Look for entries containing netdocuments, vault.netvoyage.com, or vault.netdocuments.com.
  4. Delete all matching entries.
  5. Reopen Outlook. ndMail will prompt for a fresh login.

Fix 2: Verify the Host Registry Key

NetDocuments uses a Host registry value to determine which data center to authenticate against. If your firm migrated between regions or the key was set incorrectly during deployment, login fails.

Open Registry Editor and check both of these locations:

HKCU\Software\NetVoyage\NetDocuments
HKCU\Software\NetDocuments\ndMail

Look for a Host string value. It should match your firm's NetDocuments region:

Region Host Value
US vault.netvoyage.com
US 2 us2.netdocuments.com
EU eu.netdocuments.com
AU au.netdocuments.com
DE de.netdocuments.com

If the value is wrong or missing, set it to the correct regional host and restart Outlook.

If you are not sure which region your firm uses, check with your NetDocuments administrator or log into the web interface at https://vault.netvoyage.com and note which URL you are redirected to.

Fix 3: Clear the Embedded Browser Cache

ndMail uses an embedded browser for authentication. Stale cookies in this browser cache cause login loops.

  1. Close Outlook.
  2. Delete the contents of these folders:
%LocalAppData%\NetDocuments\
%AppData%\NetDocuments\
  1. Also clear IE/Edge cached data, since some versions of ndMail use the IE rendering engine:
RunDll32.exe InetCpl.cpl,ClearMyTracksByProcess 255
  1. Restart Outlook and log in again.

Fix 4: Check Proxy and Firewall Rules

ndMail needs to reach these endpoints for authentication:

  • *.netdocuments.com
  • *.netvoyage.com
  • login.microsoftonline.com if your firm uses Azure AD SSO with NetDocuments

If your firewall performs SSL inspection, add exceptions for these domains. SSL inspection can break the OAuth token exchange and cause the "Unable to retrieve session data" error.

Fix 5: Update ndMail

Older versions of ndMail use legacy authentication methods that NetDocuments has deprecated. Check your version:

  1. In Outlook, go to File > Options > Add-ins > COM Add-ins > Go.
  2. Select the ndMail add-in and check the version number.

Compare against the latest version on the NetDocuments support portal. If you are more than one major version behind, update before troubleshooting further.

Your IT team or NetDocuments administrator can push updates via MSI deployment for the whole firm.

Fix 6: Re-register ndMail

If none of the above works, the COM registration itself may be broken. Uninstall and reinstall the ndMail add-in:

  1. Go to Settings > Apps > Installed Apps.
  2. Find NetDocuments ndMail and uninstall.
  3. Restart the machine.
  4. Download the latest installer from the NetDocuments support portal.
  5. Install and configure with the correct Host value.
  6. Open Outlook and log in.

ndMail login issues across your firm? Contact Rain City Techworks.