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Tinywall firewall may block Thunderbird with Avast

Thunderbird may be blocked from accessing IMAP/POP/SMTP if used in conjunction with Avast antivirus and Tinywall

Article mis en ligne le 12 juin 2017
par aldoniel
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 Technical chitchat

After some recent software updates, Thunderbird was unable to access IMAP/POP/SMTP while being able to connect to HTTP.

The culprit was in fact the association of Tinywall and Avast antivirus.

  • Tinywall is a convenient interface to manage the windows firewall, adding an almost user-friendly way to manage outbound filtering.
  • Avast antivirus acts as a hidden proxy and is able to perform a man-in-the-middle attack to analyze incoming and outgoing emails

I first tough that Tinywall was the culprit, because allowing outbound connections made the problem disappear.

Strangely, Tinywall was unable to detect and allow the avast service, even using its learning function (automatically, it only allowed Thunderbird).

Using WEN (Windows Firewall Notifier), (another strange windows firewall frontend whose most useful function is to display network activity in real-time) , it was evident that all outgoing traffic of Thunderbird went though Avast Service (C :\Program Files\AVAST Software\Avast\AvastSvc.exe)
(Thunderbird doesn’t even show on the screen capture)

 How to resolve this annoying trouble

  • Allow internet access to Avast Service (C :\Program Files\AVAST Software\Avast\AvastSvc.exe)

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