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Troubleshooting invalid server certificate warnings after installing Avast One

 

After installing Avast One, some third-party email clients, such as Microsoft Outlook, Mozilla Thunderbird, SeaMonkey, or The Bat!, may show that the mail server certificate is invalid when you send and receive emails.

Email Guardian (on your device) in Avast One uses an advanced scanning method for incoming and outgoing emails over SSL/TLS-secured connections. Microsoft Outlook, Mozilla Thunderbird, Sea Monkey, and The Bat! have their own certificate stores and may require extra configuration to avoid warnings about invalid mail server certificates.

This article shows you how to stop warnings about invalid mail server certificates by exporting the Email Guardian certificate then importing it into your email client's certificate store.

Export the Email Guardian certificate

  1. On your keyboard, press the Win key and E key simultaneously to open File Explorer.
  2. Copy and paste C:\ProgramData\Avast Software\Avast into the address bar and press the Enter key on your keyboard.
  3. Locate the wscert.der file in the Avast folder, and copy and paste it to your desktop.
  4. If prompted to provide administrator permission, select Continue.

The Email Guardian certificate is exported.

Each email account in your mail client needs to be configured as required by your email provider. For instructions, refer to the documentation of both your mail client and your email provider.

Import the Email Guardian certificate

If you are using Microsoft Outlook via the website https://outlook.live.com/, you do not need to import the Email Guardian certificate.
  1. In Microsoft Outlook, click the File tab.
  2. Select Options in the bottom-left corner of the screen.
  3. Click Trust Center ▸ Trust Center Settings....
  4. Click Email Security ▸ Settings....
  5. Next to Signing Certificate, select Choose....
  6. Click More choices, then select the certificate you want to use.
  7. Click OK to save.

The Avast Email Guardian certificate is now imported to Microsoft Outlook.

  1. In Mozilla Thunderbird, click ☰ Menu (three lines) ▸ Settings.
  2. Select Privacy & Security on the left panel.
  3. Scroll to the Certificates section, then click Manage Certificates....
  4. Select the Authorities tab, then click Import....
  5. Locate the Email Guardian certificate you previously exported to your desktop, select the file, and click Open.
  6. Tick Trust this CA to identify websites, then click OK.
  7. When the Certificate Manager screen appears again, click the Servers tab.
  8. Ensure that there is no entry for Avast Mail Scanner. If this entry exists, delete all certificates connected to Avast Mail Scanner in the Servers tab. Then, click OK to save the changes.

The Avast Email Guardian certificate is now imported to Mozilla Thunderbird.

  1. In SeaMonkey, click Edit ▸ Preferences....
  2. Click the arrow next to Privacy & Security to expand the section.
  3. Select Certificates, then click Manage Certificates....
  4. Select the Authorities tab, then click Import....
  5. Locate the Email Guardian certificate you previously exported to your desktop, select the file, and click Open.
  6. Tick Trust this CA to identify websites and click OK.
  7. When the Certificate Manager screen appears again, click the Servers tab.
  8. Ensure that there is no entry for Avast Mail Scanner. If this entry exists, delete all certificates connected to Avast Mail Scanner in the Servers tab. Then, click OK to close the Certificate Manager.
  9. Click OK in the Preferences window to apply the changes.

The Avast Email Guardian certificate is now imported to SeaMonkey.

  1. In The Bat!, click Tools and select Address Book.
  2. Next to Trusted Root CA, select ⋮ Menu (three dots) ▸ New Contact.
  3. Type Avast Email Guardian in the Name field and click the green tick sign in the New Certificate panel above.
  4. Ensure that Avast Email Guardian is selected and click the green Manage Certificates button.
  5. Click Import....
  6. Locate the Email Guardian certificate you previously exported to your desktop, select the file, and click Open.
  7. When the Email Guardian certificate appears in the Certificates tab, click OK to apply the changes.

The Avast Email Guardian certificate is now imported to The Bat!.

  • Avast One 24.x for Windows
  • Microsoft Windows 11 Home / Pro / Enterprise / Education
  • Microsoft Windows 10 Home / Pro / Enterprise / Education - 32 / 64-bit
  • Microsoft Windows 8.1 / Pro / Enterprise - 32 / 64-bit
  • Microsoft Windows 8 / Pro / Enterprise - 32 / 64-bit
  • Microsoft Windows 7 Home Basic / Home Premium / Professional / Enterprise / Ultimate - Service Pack 1 with Convenient Rollup Update, 32 / 64-bit


Updated on: 7/30/24

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