Hi tes.tin,
In the current settings, the SSL scanning option is now in the Geek Area settings.
To access this, open the Avast antivirus application > click "Menu" in the top right corner > click "Settings" > click "Search" in the top right corner, or use the ctrl+f shortcut > type in geek:area and press enter.
To find this specific setting in the Geek Area, click "Search" in the top right corner, or use the ctrl+f shortcut > type Mail and select the "Mail Shield: Scan SSL connections" result.