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:
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: 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: 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: 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:
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