re: My ISP (Spectrum) insists the problem is with TB They are correct, but I'm surprised they did not tell you the reason. They changed the server settings as per info at this link: https://www.spectrum.net/support/internet/spectrum-email-server-settings/

Spectrum has taken over TWC. These are the server settings you need to be using which spectrum state on their help pages.

POP The incoming mail server: mail.twc.com Incoming server port:995. Connection Security:None Authentication Method: Normal Password User name : email address

Outgoing mail server (SMTP): mail.twc.com Outgoing server port: 587. Connection Security:None Authentication Method: Normal Password User name : email address

Toad-Hall: Thanks for quick response but did not resolve. Spectrum support had me change account similarly using both port 995 and 993; but they also said to use SSL for log in. Nothing worked I tried your suggested settings also with no resolution altho my error message did change from "An error occurred . . ." to "Connection . . . timed out". As an aside, the link you provided only addresses IMAP; I have found nothing on Spectrum support that addresses POP3. Are you seeing something different?

Update 10/28/20. I had last night restored all settings to what they have been for several years (the ones under which problems occurred) and problem remained. But just like the earlier occasion, this next morning the problem self corrects. I am reluctant to change settings to what has been recommended because they did not work yesterday or earlier, and "If it ain't broke . . . ."

Additional info. Everything is now working but a new twist. I guess because of changing the pop server credentials back and forth, the "saved" password was no longer saved. So I re-saved it. I then went to look at saved passwords and the entry for the account under discussion showed the server to be "pop.nucentrix.net". which in hind sight I had seen before but not when dealing with the current problems . The account settings, show the server as "pop-server.austin.rr.com" which is what the account settings have reflected for the past 20+ years. Nucentrix was my ISP provider 20+ years ago before they went under & I switched to Time Warner (Road Runner, now Spectrum). So Thunderbird is hanging on to the old server name despite my account settings, and yet that is apparently the only way it all will work. I went to my TB Profile folder in Windows Users/AppData folder and see the attached image. The active folder is the pop.nucentrix.net folder. Is this the source of my problem? Should I change? How?

If things are changing on the provider's side, you're better off using the new recommended settings and if those aren't working, they need to fix that on their end. While the old settings are working on and off now (clearly unreliable), they may stop working entirely at any time and that won't be Thunderbird's fault.

Sorry got the port wrong. It is definately using mail.twc.com. Spectrum has taken over TWC.

The following is copied text: Server Settings Based on Domain (@example.com) Charter.net

   Incoming Email Server: mobile.charter.net
   Outgoing Email Server: mobile.charter.net

Brighthouse.com, bak.rr.com, bham.rr.com, cfl.rr.com, emore.rr.com, eufala.rr.com, indy.rr.com, mi.rr.com, panhandle.rr.com, tampabay.rr.com

   Incoming Email Server: mail.brighthouse.com
   Outgoing Email Server: mail.brighthouse.com

TWC.com and any domain ending in .rr.com not covered above (this is you)

   Incoming Email Server: mail.twc.com
   Outgoing Email Server: mail.twc.com

IMAP is the preferred method that spectrum would like to to use. But you cannot simply swap over the server settings - this would require creating a new existing mail account as IMAP. The incoming mail server: mail.twc.com Incoming server port: 993 Connection Security: SSL/TLS Authentication Method: Normal Password User name : email address

But you use POP and want to keep using POP, so this means you can change server settings. I'm sorry, but previously I did not type the correct port- it should be 110. POP The incoming mail server: mail.twc.com Incoming server port:110. Connection Security:None Authentication Method: Normal Password User name : email address

Outgoing mail server (SMTP): mail.twc.com Outgoing server port: 587. Connection Security:None but is worth trying STARTLS Authentication Method: Normal Password User name : email address

After making changes to Server Settings, you will need to restart Thunderbird.

Toad-Hall. Thanks. Problem recurred for third time after self-correcting twice. But I think problem is now solved. Spectrum had right server but wrong ports. You corrected and came up with the correct port 110 (same as existing and default for POP3 I think). What we all missed (head-slapper) is that the user name on the old server was an abbreviated form of the email address (no "@austin.rr.com). This morning I changed server to mail.twc.com, left port at 110, and changed name to full email address. And lo! It worked. Thanks for your help. I appreciate you were trying to help while Spectrum was passing the buck.