Have had the same problem on and off for years, not only with TBird.

Turns out, some providers (i.e. Comcast) are hesitant to upgrade their NETs to IPV6 ... and somehow TBird gets IPV6 addresses and tries to connect and times out.

I discovered this using Mark Russinovich's TCPview.

Solved it after I read: How to Disable/Enable IPv6 in Windows 10 https://www.howto-connect.com/disableenable-ipv6-windows-10/

Since disabling TCPV6 on my desktop, TBird is gangbuster fast, and so are my browsers.

the ".reg" to disable:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\TCPIP6\Parameters] "DisabledComponents"=dword:ffffffff

the ".reg" to enable (when availble from your provider):

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\TCPIP6\Parameters] "DisabledComponents"=dword:00000000

This was very helpful. I don't get as many and frequent not responding errors. They still come but are less frequent and quicker to go away. Thanks

To verify if your device can not access IPv6 and (in fact) that is the problem, go to: http://test-ipv6.com/

I got rid od IPv6, seemed to help. But its back to it normal not responding

any other ideas?

go to https://test-ipv6.com/

and verify if you do or do not have IPV6 connections.

If you do have IPV6 connection, then IPV6 is not the issue and you should reverse the registry values set.

If you DON'T have IPV6 connection … insure the regedit values are correctly applied … and try again.

Otherwise, don't know.

I come back as the problem continues. I run AVG and Malware Bytes. Disabled email scanning, excluded email folders. Same problem. TB has become almost unusable as the constant Not Responding errors continue. Any more suggestions?

My issue was IPV6 based as of NOV and my provider is now IPV6 enabled. so I've re enabled IPV6 on Windows 10, and TBird is super fast every time I load it, never stuck while waiting for connections.

If you have quality IPV6 connectivity (verified by: https://test-ipv6.com/) then that's not the issue.

However, as IPV6 rolls out, all those little devices sitting up there in that cloud may need to update their internal routing tables and as they do this, glitches occur. I think I experienced that for about a week or so as my provider updated their servers.

So one thing to do, as I suggested, try connection analysis using Mark Russinovich's TCPview? https://docs.microsoft.com/en-us/sysinternals/downloads/tcpview

Run it, then load TBird, and watch in real time TBird connecting TCP (or waiting).

If you watch TBird connecting (via tcpview) for each of your emails (delete all and add one at a time), you might find one that is problematic. Maybe it's a provider connection issue. Don't know.

Also, as time moves on, Windows IP caches can get old. Consider using windows command line: ipconfig /flushdns ipconfig /registerdns NETSH winsock reset catalog (then restart computer) which should flush and rebuild those caches as needed.

Otherwise, I can only offer strategies I use when such issues occur, which I'm sure you've already done. e.g.1 uninstall TBird completely, getting rid of all remnants of TBird files and folders on your computer. note: if wanting to save Local Folder stuff, zip it and delete the folders. e.g.2 try TBird on another computer, if you have one.

Sorry I don't have any more ideas. Believe me, I understand the frustration.