Outlook Error Codes

How to Fix OneNote Outlook Add-In Error 500: Server Unreachable

Huda Qurayshi Oct 13, 2026 868 views

Question details

The user is unable to use the Send to OneNote add-in in Outlook due to a persistent server error.

How to Fix OneNote Outlook Add-In Error 500: Server Unreachable

Product: Microsoft Outlook, OneNote
Device & OS: Windows
Scenario: Attempting to send emails or data from Outlook to OneNote using the built-in add-in integration.
Observed behavior: The add-in requests a user sign-in and then immediately displays a '500 Server Unreachable' error, which continues even after reinstalling Microsoft 365, rebuilding the Outlook profile, and restarting the PC.

Before you start

Verify that your internet connection is stable and ensure you have administrative privileges on your Windows computer before attempting user profile modifications.

Solution 1Recommended

Test the Add-In on a New Local Windows Account

Creating a new local user or administrator account helps determine if the server error is caused by a corrupted Windows user profile.

Often, persistent Office add-in errors that survive a complete software reinstall are tied to corrupted application data within your specific Windows user profile. Testing from a fresh account isolates the issue.

Open Windows Settings

Click the Start button, select the gear icon to open Settings, and navigate to 'Accounts'.

Add a new user

Select 'Family & other users' from the left pane, click 'Add someone else to this PC', and choose to add a user without a Microsoft account.

Create a local administrator

Follow the prompts to create a local account, then click on the new account name, select 'Change account type', and set it to 'Administrator'.

Test the add-in

Sign out of your current Windows session, log into the newly created local account, open Outlook, and test the 'Send to OneNote' add-in.

Profile Migration: If the add-in works on the new local account, your previous Windows user profile may be corrupted, and you might need to migrate your files to the new account.

Solution 2

Verify Office Versions and Submit Diagnostics

If local profile troubleshooting fails, check your specific Office build versions and contact Microsoft Support for a potential backend resolution.

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Frequently Asked Questions

Why am I getting a 500 Server Unreachable error in the Outlook OneNote add-in?

A 500 Server Unreachable error usually indicates that the add-in is failing to establish a connection with Microsoft's authentication servers. This can be caused by local network restrictions, a temporary Microsoft server outage, or corrupted application data within your specific Windows user profile.

Will reinstalling Microsoft 365 fix the OneNote add-in error?

Not always. As many users report, reinstalling Microsoft 365 or rebuilding the Outlook profile often fails to fix this specific issue because the root cause may lie in corrupted local Windows user profile settings rather than the software installation itself.

How do I find my current Outlook and Microsoft 365 build version?

To check your version, open Outlook, click the 'File' menu at the top left, and select 'Office Account' (or just 'Account'). Look under the 'Product Information' section or click 'About Outlook' to see your exact Version and Build number.

Microsoft Office Error Codes