Outlook not send or receive mails.

Check Microsoft 365 Exchange Online service health first, because the November 12 incident matches Classic Outlook showing Disconnected and failing to send or receive; if an incident remains active, wait for Microsoft’s recovery rather than rebuilding Outlook.

1. Check whether the service incident is still active

• Microsoft 365 administrator: Open Microsoft 365 admin center → Health → Service health → Exchange Online. Review both Active issues Microsoft is working on and Issue history. Service Support and Helpdesk administrators can also view this page.^1^
• Not an administrator: Check Microsoft’s public Service Health Status.^2^
• If Exchange Online is degraded, monitor the incident until Microsoft marks it resolved. An administrator generally does not need to open another service request for an already-reported incident.^3^

After recovery, close and reopen Outlook and select Send/Receive → Send/Receive All Folders.

2. Distinguish an Outlook problem from an account or service problem

Open Outlook on the web in a browser and test sending a message to yourself.

• Webmail also fails: This is not limited to Classic Outlook. Ask the Microsoft 365 administrator to check the account, license, mailbox, and Exchange Online service health.
• Webmail works: The mailbox and server are reachable; continue with the local Outlook checks below. This is the documented distinction for a Disconnected status.^4^

3. Reconnect Classic Outlook

Perform these in order and stop when the status bar changes to Connected to Microsoft Exchange:

1. In Outlook, open Send/Receive.
2. Inspect Work Offline:
   • If the button is shaded, select it once to return online.
   • If it is clear, Outlook is not deliberately in offline mode; proceed to the next step.
3. Go to File → Office Account → Sign out, close Outlook, reopen it, and sign in using the business account.
4. Go to File → Account Settings → Account Settings → Email, select the affected account, and choose Repair if that option is available.
5. Restart Outlook and test send/receive.

4. If Outlook remains disconnected while webmail works

Test without add-ins:

1. Press Windows key + R.
2. Enter:

outlook.exe /safe

3. Test sending and receiving.
4. If Safe Mode connects, go to File → Options → Add-ins → Manage: COM Add-ins → Go.
5. Disable all add-ins, restart normally, and re-enable them individually until the problematic add-in is identified.

If Safe Mode does not help, install pending Windows and Microsoft 365 updates. Outdated Outlook software and corrupted profiles are documented common causes of Microsoft 365 connection failures.^5^

As the final local-client test, create a new profile:

1. Close Outlook.
2. Open Control Panel → Mail (Microsoft Outlook) → Show Profiles → Add.
3. Add the business account and set the new profile as the default.
4. Start Outlook and allow the mailbox to synchronize.

Do not delete any .pst files. If multiple employees remain affected after Exchange Online is shown as healthy, the Microsoft 365 administrator should run the Outlook User Connectivity diagnostic or open a support request from the Microsoft 365 admin center.^5^

References

1. How to check Microsoft 365 service health
2. Service Health Status - Microsoft
3. Find and fix email delivery issues as a Microsoft 365 for business admin
4. Classic Outlook(#tab/classic-outlook)
5. Fix Outlook connection problems for Microsoft 365 account