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Troubleshooting email client warnings about invalid server certificates

 

After installing Avast Antivirus, 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.

Mail Shield in Avast Antivirus 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.

Follow the steps in this article to learn how to stop warnings about invalid mail server certificates by exporting the Mail Shield certificate, then importing it into your email client's certificate store.

Export the Mail Shield certificate

  1. Open Avast Antivirus and go to ☰ Menu ▸ Settings.
  2. Click Search in the top-right corner.
  3. Type geek:area into the search box, then select Avast Geek from the search results.
  4. Scroll to the Mail Shield section. Ensure the box next to Mail shield: Scan SSL connections is ticked, then click Perform next to Mail shield: Export certificate.
  5. Select a location to save the exported Mail Shield certificate (for example, your Windows Desktop) and click Save.
  6. Click OK in the Avast Information dialog.
  7. Import the Mail Shield certificate into your mail client.
Each individual email account in your mail client needs to be configured as required by your mail provider. Refer to your mail client's and mail provider's documentation for instructions.

Import the Mail Shield certificate

  1. In Mozilla Thunderbird, click ☰ Menu (three lines) ▸ Options.
  2. Select the Privacy & Security in the left panel.
  3. Scroll to the Certificates section, then click Manage Certificates....
  4. Select the Authorities tab, then click Import....
  5. Locate the Mail Shield certificate you previously exported from Avast Antivirus, select the file, then 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 Mail Shield 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 Mail Shield certificate you previously exported from Avast Antivirus, select the file, then 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 Mail Shield certificate is now imported to SeaMonkey.

  1. In The Bat!, click Tools ▸ Address Book.
  2. Click View, then select Certificate Address Books.
  3. Right-click Trusted Root CA, and select New Contact from the context menu.
  4. Type Avast Mail Shield in the First name field.
  5. Select the Certificates tab.
  6. Click Import....
  7. Locate the Mail Shield certificate you previously exported from Avast Antivirus, select the file, then click Open.
  8. When the Mail Shield certificate appears in the Certificates tab, click OK to apply the changes.

The Avast Mail Shield certificate is now imported to The Bat!.

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

The Avast Mail Shield certificate is now imported to Microsoft Outlook.

  • Avast Premium Security 21.x for Windows
  • Avast Free Antivirus 21.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

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