Outlook Disconnected or Trying to Connect? Fix It

New email has stopped arriving and the bar along the bottom of Outlook says "Disconnected", "Trying to connect…", "Working offline" or "Not connected". Emails sit in the Outbox. Everything else on the internet works, and Outlook on the web is fine. Colleagues may be unaffected.

When Outlook can't talk to Exchange Online, the cause is usually something simple on the PC: the offline toggle, a network or VPN change, an add-in or a damaged local data file. Here's how to work through it, quickest first.

Why This Happens

• Work Offline is on, often clicked by accident.
• Network changes: a VPN, proxy, captive Wi-Fi portal (hotels, trains, co-working spaces) or firewall blocking the connection.
• A Microsoft 365 outage affecting Exchange Online.
• Sign-in problems, where Outlook is waiting for a password or MFA it can't show.
• Add-ins that hang or crash Outlook's connection.
• A corrupted OST file (Outlook's local copy of your mailbox) or profile.

Fix 1: Turn Off Work Offline

In classic Outlook, open the Send / Receive tab and look at Work Offline. If it's highlighted, click it to turn it off. Watch the status bar: it should change to "Connected to: Microsoft Exchange" or "All folders are up to date".

Fix 2: Restart Properly

Close Outlook and check it's gone from Task Manager, then reopen it. If not fixed, restart the computer. It sounds basic, but it clears stuck sign-in prompts and network adapters.

Fix 3: Check It's Not Microsoft

1. Sign in at outlook.office.com. If email works there, your mailbox is fine and the problem is your PC or network.
2. Check Microsoft's public status page and, if you're an admin, Health > Service health in the Microsoft 365 admin centre for Exchange Online incidents.
3. Ask a colleague whether their Outlook is connected. If everyone's affected, it's likely the office network or Microsoft.

Fix 4: Check the Network, VPN and Proxy

• Disconnect from any VPN and see if Outlook reconnects. If it does, the VPN configuration needs changing.
• Public Wi-Fi: open a browser and accept any sign-in or terms page. Outlook can't connect until you do.
• Try another network, such as your phone's hotspot. If Outlook connects instantly, the original network or firewall is blocking it.
• Proxy: in an elevated Command Prompt, netsh winhttp show proxy shows any system proxy. An old or unexpected proxy can break Outlook. Ask your IT support before changing it.
• Check the date and time on your PC are correct, as secure connections fail when the clock is wrong.

Fix 5: Check the Connection Status

Hold Ctrl and right-click the Outlook icon in the system tray (near the clock), then choose Connection Status. It lists each connection and its status. Lots of failed or disconnected entries alongside a working browser point to a sign-in or profile issue rather than the network. The same menu has Test Email AutoConfiguration, which checks Outlook can find your mailbox settings.

Fix 6: Start Outlook in Safe Mode

Safe mode starts Outlook without add-ins. Close Outlook, press Windows + R, type outlook.exe /safe and press Enter. If Outlook connects in safe mode:

1. Close it and open Outlook normally.
2. Go to File > Options > Add-ins, choose COM Add-ins next to Manage and click Go.
3. Untick add-ins one at a time, restarting Outlook each time, until you find the culprit. Common offenders are old CRM, PDF, telephony and email signature add-ins.

Fix 7: Repair Office

Go to Settings > Apps > Installed apps, find Microsoft 365, choose Modify and run Quick Repair. If that doesn't help, try Online Repair, which reinstalls Office and takes longer.

Fix 8: Rebuild the OST File or Profile

Your email is stored in Exchange Online. The OST is only a local copy, so rebuilding it is safe.

1. Close Outlook.
2. Press Windows + R, enter %localappdata%\Microsoft\Outlook and press Enter.
3. Find the .ost file named after your email address and rename it, for example by adding .old to the end.
4. Open Outlook. It creates a new OST and downloads your mailbox again, which can take a while for large mailboxes.

If that fails, create a new profile: Control Panel > Mail (Microsoft Outlook) > Show Profiles > Add, set it as the default and open Outlook.

What About the New Outlook?

The new Outlook for Windows works more like Outlook on the web and doesn't use an OST file or COM add-ins. If it shows as offline, check your network, sign out and back in, and try the toggle back to classic Outlook (or the reverse) to see whether one version works.

For Your Microsoft 365 Admin

• Check Service health and message centre posts for Exchange Online.
• Check the user's Entra sign-in logs for failed or interrupted sign-ins, which can leave Outlook disconnected.
• Make sure firewalls, web filters and VPN split tunnelling follow Microsoft's published Microsoft 365 URLs and IP ranges, especially the "Optimize" category for Exchange Online.
• Microsoft's Remote Connectivity Analyzer (testconnectivity.microsoft.com) can test Outlook connectivity and Autodiscover from outside your network.

How to Stop It Happening Again

Repeated disconnections usually mean something in the environment needs fixing: an old VPN that sends everything through the office, a web filter that doesn't know about Microsoft 365, out-of-date Office builds or a pile of old add-ins. Keeping Office updated through a managed channel, removing unneeded add-ins and configuring networks according to Microsoft's guidance stops most of these before users notice.

When to Call in Help

If Outlook keeps disconnecting, or the whole office loses email, our IT support team can find the cause quickly, and our managed IT service keeps devices, networks and Office consistent. Want to know how healthy your setup is? Try our free IT health check, or get in touch.

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