Invalid Security Certificate Error when using AVAST



If you use Avast anti-virus software, you may see an error message about an invalid security certificate when you're setting up a google account or when you're fetching mail from a google account.

The issue is one of Avast's Mail Shield settings that scans connections which use the SSL security protocol. Since SSL provides a secure connection, this feature of Avast offers extra protection for connections that should already be secure. 


To solve the invalid certificate issue:

  1. Launch Avast.
  2. Click SETTINGS, and then select the Active Protection tab.
  3. Click Mail Shield's Customize button to display the SSL Scanning window.
  4. Uncheck Scan SSL connections.
  5. Exit Avast.

Some customers report that they've been able to add IMAP servers to NOT scan, which could also solve the problem.

Alternative Solution

A Postbox customer also shares the following:

  • Export the Mail Shield certificate from Avast Antivirus 
  • Open the Avast user interface and click ☰ Menu ▸ Settings. 
  • Select General from the left panel, then click Troubleshooting ▸ Open old settings. 
  • Select Components from the left panel, then click Customize in the Mail Shield panel. 
    Select SSL scanning from the left panel and ensure the box next to Scan SSL connections is ticked, then click Export certificate. 
  • Select a location to save the exported Mail Shield certificate (for example, your Windows Desktop) and click Save. 
  • Click OK in the Avast Information dialog. 
  • Import the Mail Shield certificate into Postbox.
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