This error commonly appears in Outlook when the email client fails to communicate with the mail server, usually due to incorrect configuration, a firewall blocking the connection, or port-related issues.

Step 1: Check Internet Connection

Make sure you have a stable internet connection. Try visiting a website (e.g., www.google.com) to confirm.

Step 2: Verify Email Account Settings in Outlook

1. Open Outlook

2. Go to File > Account Settings > Account Settings

3. Select the affected account and click Change

4. Double-check the following:

   • Incoming mail server (IMAP/POP3): mail.your-domain.com (depends on your provider)

   • Outgoing mail server (SMTP): mail.your-domain.com

   • Username: your full email address (e.g., user@domain.com)

   • Password: your correct password

5. Click on More Settings > go to the Outgoing Server tab and ensure:

   •  “My outgoing server (SMTP) requires authentication” is checked

   • Select: “Use same settings as my incoming mail server”

6. Go to the Advanced tab and verify the following ports:

   • IMAP: 993 with SSL enabled

   • SMTP: 587 with TLS enabled (or 465 with SSL, depending on the provider)

 Step 3: Temporarily Disable Antivirus or Firewall

Sometimes, antivirus or firewall software can block the ports used by Outlook.

1. Open your antivirus (e.g., Bitdefender, Avast, Norton)

2. Temporarily disable email protection and the firewall

3. Try sending/receiving emails again

   Warning: Do not keep your antivirus disabled. If Outlook works after disabling it, add exceptions for Outlook and the required ports in your antivirus/firewall settings.

Step 4: Repair Microsoft Outlook

1. Go to Control Panel > Programs and Features

2. Find Microsoft Office in the list

3. Right-click > Change > Choose Quick Repair or Online Repair

 Step 5: Test Outlook in Safe Mode

1. Press Win + R, type outlook.exe /safe, and press Enter.

2. If Outlook works in Safe Mode, disable all add-ins:

   • Go to File > Options > Add-ins

   • At the bottom, where it says “Manage: COM Add-ins”, click Go…

   • Uncheck everything and click OK. Then try starting Outlook normally.

 Step 6: Check the .PST or .OST Data File

Corrupted data files can prevent proper email synchronization.

1. Close Outlook

2. Open Control Panel > Mail > Data Files

3. Note the location of the .PST/.OST file in use

4. Run the ScanPST.exe utility:

   • Default path: C:\Program Files (x86)\Microsoft Office\root\OfficeXX\ScanPST.exe
     (XX depends on your Office version: e.g., Office16, Office19, etc.)

   • Scan and repair the .PST/.OST file if errors are found.