I used Thunderbird email software for more than a decade now, and never had an issue with receiving emails from Gmail.
In the summer of 2019 I started to get this error: “connection to server pop.gmail.com was reset”.
I use Windows 10 and the latest version of Thunderbird, which now it’s 60.9.0. I also use AVG Free Antivirus, current version 19.8.3108.
These are the solution that worked for me.
The last solution is a definitive solution.
1. Deactivate Email Shield in AVG.
I searched Google for a solution and I arrived on some forums that related the error to a conflict with AVG antivirus.
It was suggested to deactivate the Email Shield under “Web & Email” basic protection, which solved the problem temporary.
I also noted, that I reactivated the Email Shield and restarted to computer, the issue was also solved.
But if you shutdown the computer, when you start it again, the issue reappears.
2. Clear AVG installation and reinstall AVG Free Antivirus.
This solution worked for me, but just one time. Then the issue reappeared.
3. Set ‘network.dns.disableIPv6’ to True in Thunderbird config editor.
In Thunderbird – Tools – Options – Advanced – General – Config editor. When you click on Config editor you are prompted to accept the risk of editing these configuration settings. Click “Ok” to accept it, then you will see the Config editor window.
At the top search for ipv6, then double click the entry for network.dns.disableIPv6 to set it to True.
This solved the issue permanently. See the help images below.
I found this solution by Dave Trapmore in Google forum. He also suggested that you can also set ‘network.dns.ipv4OnlyDomains’ to ‘gmail.com’ to make it work.
Thank you, Dave!
Note: Thunderbird logo provided by Commons Wikimedia.