[FIX] Thunderbird ‘Connection was Reset’ Error

Some Thunderbird users are getting the ‘Connection was Reset‘ error sporadically after their email client fails to connect to the email client. This problem is commonly reported to occur with Gmail.

‘Connection to Server was reset’ error with Thunderbird

As it turns out, there are several different causes that might end up causing this error. Here’s a shortlist of potential culprits that might trigger this problem:

  • Avast’s Mail Shield is blocking Thunderbird – Avast Internet security (the Premium version) includes an email protection module that is known to confirm with Thunderbird. In this case, the only thing you can do to fix the problem is to disable the Mail Shield feature from Core Shield inside the Settings menu of Avast.
  • A modified version of Thunderbird – According to some affected users, this problem can also occur if you’re using a modified version of Thunderbird. In this case, chances are the native Windows Firewall will threaten the executable as a potential security threat and block it. To prevent this from happening, you’ll need to whitelist the executable from the Windows Firewall settings menu.
  • AVG Shield is blocking Thunderbird – Another module that is reported to cause an issue with Thunderbird is the email protection feature on AVG Antivirus. Just like with Avast Mail Shield, this security feature is enabled by default, so the only way to solve this conflict is to disable it from the Settings menu of your AVG antivirus.
  • Overprotective AV Suite – In some cases, the reason why Thunderbird will trigger this error is an instance where the main executable is blocked by an overprotective suite or firewall. if this scenario is applicable, you can fix this issue either by whitelisting the Thunderbird executable or by uninstalling the overprotective suite altogether.

Method 1: Disabling Mail Shield by Avast (if applicable)

One of the most common culprits that are known to cause this issue is the mail scanning feature on Avast called Mail Shield. This security feature is known to interfere with several different email clients (not just Thunderbird).

Several affected users have managed to fix this problem by accessing the setting of Avast and disabling Mail Shield so that it could no longer interfere with the active email client.

If this scenario is applicable and you don’t know how to disable the Mail Shield feature in Avast, follow the instructions below:

  1. Open your Avast program on your computer. You can do this by double-clicking on the desktop icon or by clicking its icon in the system tray.
  2. From the main dashboard of the Avast program, click on Settings from the left navigation pane to open up Avast Settings window.
  3. Next, from the new list of options, click on the  Protection tab to view all active protection components.
    Accessing the Protection tab in Avast Settings
  4. Move over to the right-hand tab, select Core Shields, and select Mail Shield under Configure Shield Settings.
  5. Once you manage to find the Mail Shield component, uncheck the box associated with Enable Mail Shield and then click on Stop permanently from the new menu to disable it.
    Disabling Mail Shield

    Note: If you want to disable the Mail Shield temporarily so you can confirm if your security suite is causing this, you can choose to Stop for 10 minutes, Stop for 1 Hour or Stop until restart of computer.

  6.  Click Ok to close the Avast Settings window.
  7. Once Mail Shield has been disabled, repeat the action in your email client that was previously causing the problem and see if the error stops occurring.

In case the same ‘Connection was Reset‘ error is still appearing, move down to the next method below.

Method 2: Whitelisting the Email Client

If you’re using a modified version of Thunderbird, it’s also possible that you’re seeing this error due to the fact that Windows Defender ended up blocking the connections bridged by the Thunderbird due to a false positive.

Several users facing the same issue have confirmed that they managed to avoid the ‘Connection was Reset‘ error by whitelisting the main Thunderbird executable from Windows Firewall.

If this scenario looks like it could be applicable, follow the instructions below to whitelist the email client:

  1. Open up a Run dialog box by pressing Windows key + R. Next, type ‘control firewall.cpl‘ inside the text box and press Enter to open up the classic interface of the Windows Firewall.
    Accessing the Windows Defender Firewall
  2. Once you’re inside the Windows Defender Firewall menu, use the menu on the left to click on Allow an app or feature through Windows Defender Firewall.

    Allowing an app or feature through Windows Defender
  3. Inside the Allowed app menu, click on Change Settings button. Next, click on Yes at the UAC (User Account Control) prompt to allow admin access to the app.
    Changing the Settings of the Allowed Items in Windows Firewall
  4. Once you have admin access, scroll down through the list of applications and see if Thunderbird is present among the list of allowed items. If it’s not, click on Allow another app and navigate to the location where you installed Thunderbird.
  5. Once you’ve ensured that the main Thunderbird executable is added, ensure that you check both the Private and the Public boxes associated with the Thunderbird entry before saving the changes.

If the same problem is still occurring, move down to the next potential fix below.

Method 3: Disable AVG Shield (if applicable)

As it turns out, this problem can also occur due to a conflict with AVG Internet security.

If you’re using this security suite, you should start by trying to deactivate Email Shield (under Web & Email basic protection). This fix was confirmed to be effective by a lot of users that we’re encountering the Connection was Reset with Thunderbird.

If you’re using AVG Antivirus and you don’t know how to disable AVG Shield, follow the instructions below:

  1. Open the AVG user interface. You can do this either by double-clicking on the utility executable, by double-clicking the tray bar icon, or by searching for the suite using the start menu.
  2. From the main AVG User Interface, click on Menu (top-right section), then click on Settings from the newly appeared context menu.
    Accessing the Settings menu
  3. Once you’re inside the Settings menu, click on Basic Protection from the menu on the left, then choose Email Shield from the associated context menu that just appeared.
    Accessing the Email Settings menu
  4. From the Email Shield menu, simply click on the On/Off toggle to disable the security feature and confirm when asked to do so.
    Disabling the Email Shield functionality in AVG
  5. Restart your computer to ensure that the Email Shield feature is no longer interfering, then open Thunderbird again and see if the problem is now resolved.

This is known to solve the problem temporarily, but if you want to avoid this same error in the future, you need a more permanent solution.

Users that found themselves in a similar situation have reported that the only way they’ve been able to fix this problem is to uninstall the security suite altogether. Follow the next method below to do this.

Method 4: Uninstall Overprotective 3rd-party AV (if applicable)

If this problem is still occurring despite following every other fix above and you’re using a 3rd party tool, you should consider the fact that you’re dealing with an overprotective suite that is blocking Thunderbird from communicating with the email server.

In this case, the only thing you can do to ensure that you’re not dealing with an AV interference is to temporarily uninstall it from your system and see if the apparition of the Connection was Reset error is still occurring.

Here’s a quick guide on uninstalling the potentially overprotective suite:

  1. Press Windows key + R to open up a Run dialog box. Next, type ‘appwiz.cpl’ inside the text box and press Enter to open up the Programs and Features window.
    Type appwiz.cpl and Press Enter to Open Installed Programs List
  2. Once you’re inside the Programs and Features menu, scroll down through the list of installed programs and find the security suite that you suspect is interfering with Thunderbird.
  3. After you locate the 3rd party AV suite that you want to uninstall, right-click on it, and choose Uninstall from the context menu.
    Uninstalling your antivirus
  4. Inside the uninstallation screen, follow the on-screen instructions to complete the uninstallation.
    Note: If you want to be extra sure that you remove every left-behind file of your AV, you need to deep clean your AV directories.
  5. Once the security suite has been uninstalled, restart your computer and see if the error is fixed at the next computer startup.

Kevin Arrows

Kevin Arrows is a highly experienced and knowledgeable technology specialist with over a decade of industry experience. He holds a Microsoft Certified Technology Specialist (MCTS) certification and has a deep passion for staying up-to-date on the latest tech developments. Kevin has written extensively on a wide range of tech-related topics, showcasing his expertise and knowledge in areas such as software development, cybersecurity, and cloud computing. His contributions to the tech field have been widely recognized and respected by his peers, and he is highly regarded for his ability to explain complex technical concepts in a clear and concise manner.