Major outlook issues on OSX Tahoe

Hi @Zeki,

Thanks for the detailed answers.

Based on what you’ve confirmed, this is not an Exchange issue and not an account issue. It is local to Outlook for Mac on this M1 device, with macOS 26.3.1 + network filtering (Zscaler) being the key factors.

Because OWA and Windows work fine, your Exchange mailbox and account are healthy. The "No Internet" error you're seeing during setup could be caused by the Zscaler Client Connector losing its ability to properly work with macOS Tahoe's new Liquid Glass networking stack.

You can try the following steps to fix the "No Internet" block and get Outlook 26.x authenticated:

1. Fully unload Zscaler (not just “disconnect”)

Even if Zscaler is "Off," its System Extension (the filter) is likely still active in the macOS kernel. On Tahoe 26.3.1, these filters are currently "swallowing" the authentication packets meant for Microsoft's login servers.

• Go to System Settings > Network > Filters.
• Look for Zscaler (and any other content filters).
• Even if they say "Running," try to Disable them manually or click the - (minus) to remove them temporarily.
• Restart your Mac. Try to add the account again before Zscaler re-engages.

Additionally, you can go further and run these commands in Terminal:

To Unload Zscaler Services:

# This stops the background tunnel and service agents

sudo launchctl bootout system/com.zscaler.service 
sudo launchctl bootout system/com.zscaler.tunnel

To Fully Kill the UI Process:

# Prevents the app from auto-restarting while you setup Outlook
killall "Zscaler"

Note: Once you have successfully added your Outlook account and the first sync starts, you can restart Zscaler by rebooting or running open -a "Zscaler".

2. Bypass Tahoe's "Private Relay" & "IP Tracking"

Tahoe 26.3.1 has intensified "Limit IP Address Tracking," which masks your Mac's identity from Exchange's conditional access.

• Go to System Settings > Network > Wi-Fi (or Ethernet).
• Click Details for your current network.
• Ensure Limit IP Address Tracking is OFF.
• 
• Verify in iCloud Settings that Private Relay is also OFF. These features often conflict with Zscaler’s tunnel, leading Outlook to believe there is "No Internet."

3. Clear the "Identity" Keychain cache

Since you've already uninstalled and reinstalled, you've likely cleared the app, but not the Microsoft Professional Identity tokens stored in the macOS Keychain, which Tahoe is now protecting more strictly.

• Open Keychain Access.
• Search for and delete all entries containing:
  • MicrosoftOffice15
  • com.microsoft.Outlook
  • com.microsoft.adalcache
  • Microsoft Professional Identity
• Crucial: Search for adal and delete those tokens; these are the specific "Modern Auth" tokens that 26.3.1 is failing to refresh.

4. Create a fresh Outlook profile:

If the standard "Add Account" screen is failing, bypass it by creating a new profile container entirely.

• Quit Outlook.
• In Finder, go to Applications, right-click Microsoft Outlook, and select Show Package Contents.
• Navigate to Contents > SharedSupport and open the Outlook Profile Manager.
• Click the + to create a new profile (name it "Test").
• Click the "Gear" icon and select Set as Default.
• Open Outlook. It will be completely empty. Try adding your account here.

More information at: Manage profiles or identities in Outlook for Mac - Microsoft Support

The steps above address basic network connectivity troubleshooting; however, it’s important to note that many users are currently reporting issues related to the macOS 26.3.1 update. I recommend reaching out to your IT administrator and asking them to investigate this further, as the issue may be related to the operating system update rather than a standard connectivity problem. The admin should open a support case with Microsoft Support, as backend diagnostics may be required. They can reach out to Microsoft Support through the Microsoft 365 Admin Center on your behalf so Microsoft can collect logs and investigate your issue. 

Microsoft also provides customer service phone numbers based on your region. You can find the appropriate contact number here: Customer service phone numbers - Microsoft Support 

This route ensures that a Microsoft support engineer can initiate a remote session to investigate backend configurations, run advanced diagnostic tools, and, if necessary, escalate the case to specialized teams with access to internal systems and logs. These backend resources are essential for resolving issues that go beyond what’s visible in the user interface.

As community moderators, we’re here to guide you, but due to privacy and security limitations, we don’t have access to the backend tools required for a full resolution. For this reason, contacting Microsoft Support via the Admin Center is the most secure and efficient way forward.

I hope this helps you resolve the issue quickly. I’m glad to assist and truly hope the information provided has been useful. Please feel free to reach out anytime if you need further assistance.  

Thank you for your kindness and contributions to the forum.

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Does not work and I cannot use the contact support options as outlook complains about a network error!!

Use a step-by-step approach to isolate whether this is Outlook for Mac itself, the Exchange connection, or the macOS environment.

1. Verify Outlook is online and connected

• In Outlook for Mac, on the Outlook menu, ensure Work Offline is not checked.
• Go to Tools → Accounts and check the Exchange account status in the left pane. If the indicator is orange, Outlook is not properly connected to Exchange.
• If the account previously worked, try accessing the same mailbox via Outlook on the web to confirm the Exchange service itself is healthy. If Outlook on the web also has issues, contact the Exchange admin to check server status.

2. Check for general send/receive and network issues

• If there are intermittent send/receive failures, verify basic account settings under Tools → Accounts (email address, username, password, and any required SSL/port settings) as described for Outlook for Mac connectivity issues.
• If the environment uses a firewall or proxy, confirm with the network admin that connections to Exchange (and any SMTP/IMAP endpoints if applicable) are not being blocked or throttled. For POP/IMAP accounts, an alternative SMTP server may be required if the current one is blocked.

3. Repair possible cache corruption for the Exchange mailbox Corrupted local cache can cause sync and connectivity symptoms even when the server is fine.

• Ensure the Mac is online and can reach the Exchange server.
• In Outlook’s folder list, Ctrl+click or right‑click the problematic Exchange folder (for example, Inbox) and select Properties.
• On the General tab, choose Empty Cache.
• Outlook will clear the local copy and re-download items from Exchange.
  • Caution: this removes anything not yet synchronized with the server (for example, unsynced changes or certificates), so ensure important data is on the server before doing this.

4. Update Outlook for Mac to the latest build

• Many stability and connectivity issues are resolved in newer builds. Update Office for Mac to the latest version, then test again.
• If using the “New Outlook” experience, note that some issues are known and fixed over time; staying current is important.

5. Check for known Outlook for Mac issues

• Review the list of Fixes or workarounds for recent issues in Outlook for Mac and confirm whether the current symptoms match any of the documented issues. If so, apply the recommended workaround or ensure the build that contains the fix is installed.

6. If issues persist across New and Classic Outlook

• Since resetting, clearing cache, uninstalling, and reverting to Classic have already been tried, and if the Exchange server and network are confirmed healthy, use the in-app Help → Contact Support option in Outlook for Mac to open a support request. This routes logs and environment details directly to support for deeper analysis.

If none of the above stabilizes connectivity and Outlook on the web works reliably, the problem is likely specific to Outlook for Mac on this device, and working with Microsoft support via Contact Support is the next step.

References:

• I'm not receiving email or other items in my Exchange account in Outlook for Mac
• I can't send or receive messages with Outlook for Mac
• Fixes or workarounds for recent issues in Outlook for Mac
• Outlook for Mac
• Fix Outlook connection problems for Microsoft 365 account