How Do I Fix SMTP Error 421?

The SMTP error 421 is a common one with Gmail accounts configured in the Microsoft Outlook email client.

SMTP Error 421

Remove and readd the email account:

  • Step 1: Start the Microsoft Outlook email client on your computer, navigate to the File menu, and click the Account Settings option.
  • Step 2: Go to the Email tab, choose the email address of your account, and click the Remove option.
  • Step 3: This will remove the selected email completely.
  • Step 4: To reconfigure the email account, click the New button.
  • Step 5: When the Add Account window opens, select the radio button beside the Email Account option and provide the Your Name, Email Address, Password, and Retype Password fields.
  • Step 6: Select the Next option in the Auto Account Setup window.
  • Step 7: If the Congratulations message appears on the screen, it indicates that the email configuration is done successfully.
  • Step 8: Click the Finish option in the Add Account window.
  • Step 8: Use this procedures to fix the SMTP Error 421.

SMTP port number:

  • Step : 1 Open the Account Settings window, select your email account, and click the Change button.
  • Step : 2 After you click the More Settings button, the Internet Email Settings dialog window will be displayed on the screen.
  • Step : 3 Click Advanced, type 465 in the Outgoing Server (SMTP) option, and choose the SSL option from the ‘Use the following type of encrypted connection’ drop-down menu.
  • Step : 4 Firewall interference:
  • Step : 5 Disable the third-party antivirus or firewall program installed on your computer.
  • Step : 6 In the main window of the Microsoft Outlook email client, click the File tab and choose the Options option followed by the Add-ins option.
  • Step : 7 Search for the antivirus plug-in installed on your computer and click the Go button at the bottom of the screen.
  • Step : 8 Deselect the checkbox next to the selected plug-in.
  • Step : 9 This will help to prevent the firewall/antivirus plug-in interference with the email server.

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