Classic Outlook has stopped sending and receiving emails

Classic Outlook stopping mail flow is usually caused by connection, profile, or program issues rather than whether Microsoft 365 is licensed or installed. Existing Office files (Word, Excel, etc.) are not removed or changed if Microsoft 365 Apps are later installed; they remain on disk and can still be opened. The immediate focus should be restoring send/receive in classic Outlook.

Work through these steps in order:

1. Confirm Outlook is actually connected

• In classic Outlook, look at the status bar at the bottom.
• If it shows Disconnected, Working Offline, or Trying to connect…, Outlook is not talking to the mail server.
• Go to the Send/Receive tab → Preferences group → select Work Offline once to toggle back online.
• Then choose Send/Receive or open and resend any stuck messages.

2. Verify internet access from Windows Even if other devices work, confirm this PC has full connectivity:

• Open a browser on the same PC.
• Browse to http://www.microsoft.com and http://www.bing.com.
• If these fail, follow the guidance in Fix network connection issues in Windows from the article.

3. Check for oversized or stuck messages Large attachments can block the Outbox and stop all subsequent mail:

• In Outlook, open the Outbox.
• Start with the oldest message. If any message has an attachment larger than about 20 MB, delete the attachment.
• Either attach a smaller file or use a link instead (see Reduce attachment size to send large files with Outlook in the article).
• Try sending again.

4. If a password was recently changed If the account password was changed on the provider’s website, it must also be updated in Outlook:

• Follow Reset a forgotten Microsoft account password if this is a Microsoft account.
• Then update the account credentials in classic Outlook’s account settings.

5. Check antivirus email scanning Some antivirus products block send/receive when they detect an issue:

• If antivirus email scanning is enabled, consult the antivirus help desk or documentation to temporarily disable email scanning and test again.

6. Repair classic Outlook and the Outlook profile If the program or profile is damaged, mail flow can stop:

• Run an Office repair as described in Repair an Office application.
• If needed, repair or recreate the Outlook profile using Fix your Outlook email connection by repairing your profile and Create an Outlook profile.

7. Test Outlook in Safe Mode Add-ins can block sending/receiving:

• Press the Windows key, type outlook.exe /safe, press Enter.
• If mail works in Safe Mode, create a new Outlook profile and disable problematic add-ins.

8. Use Microsoft’s troubleshooters

• Go to the Classic Outlook troubleshooters page and run the relevant troubleshooter for send/receive issues.

If none of the above resolves the issue, use the contact support option from the Outlook support article for direct assistance.

Installing Microsoft 365 Apps later will not delete or corrupt existing Office files; they remain accessible and can be opened in the newer apps. The key is to restore Outlook connectivity and profile health first.

References:

• I can't send or receive messages in Outlook
• Issues sending and receiving email