I think you are suffering from a new anti virus program and it's attendant firewall more than Thunderbird issues.

beyond that you probably need to revisit your server settings. road runner updated them some years ago to not use those locality based server names being replaced with mail.twc.com

See https://www.timewarnercable.com/en/support/faqs/faqs-internet/e-mailacco/incoming-outgoing-server-addresses.html.

Thanks for the Reply. I contacted TWC and reviewed the settings. He suggested that the problem was that I was not using TWC as the Default Outgoing Server? After changing the behavior of Thunderbird it did not change and I still cannot select any other folder or account. The mid menu box is not there for Reply/Forward/Delete etc.. The Time Out of POP TWC server message is still arriving 10 seconds or so after opening the program. All account settings appear normal. Only Gmail account is using IMAP server. I read the TWC info about POP vs IMAP set up and I saw this input while talking to the TWC rep, but he had no input as to whether selecting both or one or the other made any difference. Evidently IMAP is the better method, but my other accounts have no issues with that. This seems to be a "Catch 22" issue. The problem began with the necessity of reinstalling Thunderbird after a System Restore. I had to install Thunderbird again and selected what I thought would be a 64bit edition, but Ver 52.5.0 only installs as 32bit and with the problems of not running correctly. I like the email client, but now something has gone wrong with the installation. I have adequate Virus protection and nothing is advising any problems.

Follow Update. I had the idea to see if I could find a Previous Version of Mozilla Thunderbird to install. The mozine page had a long article about how to do that. There was a link to download Version 45.0.8 from March 2017. Save to Desktop and then used the advice to make sure that my Update Auto setting was turned off in Mozilla T, then I Uninstalled through Control Panel Program/Features. Clicked on the Desktop file to install the old version and POOF! all went well and my interface for that version is working as before! Now I need the courage to take the Help recommendation to UPDATE to Version 52.5.0....?????

The install of the latest version 52.5.0 returned the same problem issues as before. For my computer or others? - This update needs to be checked and revised. I get the POP Server Time Out message using the later version of Thunderbird and cannot navigate the various inboxes either. Broken Version in my opinion as I've not made any System setting changes in the program or to my Windows 7 computer configurations.

Fwilburn said

The install of the latest version 52.5.0 returned the same problem issues as before. For my computer or others? - This update needs to be checked and revised. I get the POP Server Time Out message using the later version of Thunderbird and cannot navigate the various inboxes either. Broken Version in my opinion as I've not made any System setting changes in the program or to my Windows 7 computer configurations.

I dare say you have defective anti virus/firewall software. Most users of the fine line of Norton products have these inability to connect problems with every version update of Thunderbird, but they are not alone. You will need to check that software is allowing Thunderbird 54.whatever version you have installed, access to the internet with out restriction. Check your anti virus/ security suite does not have any add-ons installed in Thunderbird. They are notorious for producing add-ons that just do not work with more than one version. ALso disable an email scanning.

Matt thanks for your interest, but you make a gross assumption that I have Norton Anitvirus program installed on my computer. I have not used that program for many years past as it and McAfee were too invasive and expensive. I use a Trojan Remover program and Microsoft Essentials for my computer security scans. Neither have ever had a program installation or usage problem. The only add-ons I use are German and Italian Dictionary. When I download and install a previous version of Thunderbird and it works fine, but is way out of date, then I update to the latest version I keep having the same program "lock up" after upgrading to Version 52.5.0 with the Server POP.kc.rr timing out error. Whatever or However that is screwing up the installation or program is unknown. My only conclusion is that the latest Mozilla Update has a problem. Never had any problems previously with any update to Mozilla. So I wait for the next update to see if it will run properly. Furthermore, I may try dumping the Road Runner TWC email account to see if that helps. I am not using and did not accept the advice from TWC Support to use them as the Default server for all of my email services from either iCloud, ATT, or Gmail. If that account connection is the problem I will advise. I also have NO Problem with Internet services connection from TWC, ONLY Mozilla !!! No issues either on my Apple devices with Apple email client.

No I do not make any assumption about what you have installed, what I assume is you have security software. A firewall to be specific that allows one version of Thunderbird to access the internet, but not another. If that is in error, you will probably be one of a few , as Windows has had a firewall built in since Vista and it is turned on by default. The windows firewall works like all firewalls in the past. Blocking and rerouting ports and rarely causes trouble (that I have seen here.) but it can cause trouble by blocking or redirecting the ports used to get mail.

Just about all security companies in a vain effort to make themselves appear to be doing something useful start out with application firewalls that allow and block applications access to the internet. Thunderbird is a frequent victim of this sort of white listed security. If I am mistaken there, sorry. but most issues with connectivity post update are firewalls.

You are however still talking about a server named. POP.kc.rr. That you have chosen to ignore the need to use current server configurations advertised by your mail provider makes everything null and void really.

Is that server using obsolete security protocols or cyphers that have been removed from the current version of Thunderbird. Possibly. TWC has nothing to gain in upgrading security on servers it is in the process of decommissioning.

This is what I get when I search of that server.

ping kc.rr.server.com
Ping request could not find host kc.rr.server.com. Please check the name and try again.

This is what I get when I search for the advertised mail server.

ping mail.twc.com

Pinging dnvrco-twc-vip.email.rr.com [107.14.73.68] with 32 bytes of data:
Reply from 107.14.73.68: bytes=32 time=243ms TTL=42
Reply from 107.14.73.68: bytes=32 time=240ms TTL=42
Reply from 107.14.73.68: bytes=32 time=241ms TTL=42
Reply from 107.14.73.68: bytes=32 time=270ms TTL=42

Ping statistics for 107.14.73.68:
   Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
   Minimum = 240ms, Maximum = 270ms, Average = 248ms

So mail.twc.com resolves to dnvrco-twc-vip.email.rr.com but you are using neither server names.

Thanks for the clarification on the Antivirus vs Firewall factor. Not sure what to do about the Windows "Firewall" settings. More confusing is the Ping situation with TWC server(s). When I contacted Support at TWC the agent only asked about my connection set up for kc.rr.com server. That is the same setting that I had been using. No mention of the other or newer Server connection. Possibly more importantly you mention the Com Port issues. I recently installed a StarTech 2 port RS232/422 PCI serial interface card. I worked with 2 technicians who were very knowledgeable in assisting to set the Drivers and Com Ports. Com 1 was the only one that was not changed as it show In Use, but with all the attempts to install the drivers correctly and connect to the correct Com Port for my installation the 1 - 10 ports were checked and verified. Again the connections for ATT, Gmail, and iCloud function OK as does the Internet from TWC. I will accept your position that it is not a problem with the latest Mozilla software program. But which TWC server is correct so that the Ping factor does not 'Time Out' must be close to the answer to correct the problem. OR something with the Firewall setting which I can attempt to figure out to see if it is blocking something... not an expert on that mystery. I appreciate your assistance for recommendations to resolve the problem as I would like my system to return to the normal Mozilla Update status if I can fix the problem. Best Regards.

I am and have been using the TWC server settings as advertised. You missed the point about their suggesting that I use their server as my Default Server for ALL email transactions - send and receive in Thunderbird? I've always used the primary email account of ATT Yahoo Sbcglobal for years without any Default Server issues. Just changing now to TWC / Spectrum Server as the Default, which I tried, does not make any sense to me and it did not change anything when I did. Still waiting to see if a new Update will resolve this issue. I did review all Windows Firewall settings with Mozilla checked as Normal Network Private setting. Public is NOT checked as this is a home PC. Baffled.

Hi Matt. Well I just Removed the TWC Road Runner Email account from Thunderbird then Updating to the New 52.5.0 revision. Now the program is working as Normal or as expected. Not sure what the issue is or was with TWC/Spectrum/Servers or Ping situation? But the account is presently removed. I will probably try reinstating the account in Thunderbird to see if the problem returns again. I still have not problems receiving the emails on my iPad or iPhone from that account using the Apple Mail client App. Thanks for your suggestions, if you have further comments or Help assistance regarding this problem I am interested in learning what may have been the problem or what to do if it returns again. Regards FRW

One more Update. I reinstalled the TWC Road Runner account in Thunderbird and ran a test. This was using a POP3 setting when setting up even though it only shows POP when checking the settings. IMAP was a choice but I was not sure if it would work under that setting, something about sending mail to "folders"? The account installed and after turning off Thunderbird and reopening all seems to be functioning Normally with access to all functions in Thunderbird and receiving mail to the re-established account as expected.